Hope this clear things up.

Module is appearing in System -> Configuration -> Advanced (under Advanced Group) and is enabled

Cache was deleted with rm -r var/cache
Session was deleted with rm -r var/session
 stat -c "%a %n" app/code/local/Proweb/CustomClass/*
755 app/code/local/Proweb/CustomClass/Block
755 app/code/local/Proweb/CustomClass/Model
755 app/code/local/Proweb/CustomClass/etc
755 app/code/local/Proweb/CustomClass/sql


app/etc/modules/Proweb_CustomClass.xml:
<?xml version="1.0"?>
<config>
    <modules>
        <Proweb_CustomClass>
            <active>true</active>
            <codePool>local</codePool>
        </Proweb_CustomClass>
    </modules>
</config>

app/code/local/Proweb/CustomClass/etc/Config.xml

<?xml version="1.0"?>
<config>
    <modules>
        <Proweb_CustomClass>
            <version>1.0</version>
        </Proweb_CustomClass>
    </modules>
    <global>
        <blocks>
            <Adminhtml>
                <rewrite>
                    <Catalog_Product_Edit_Tab_Options_Option>
                        Proweb_CustomClass_Block_Adminhtml_Option
                    </Catalog_Product_Edit_Tab_Options_Option>
                </rewrite>
            </Adminhtml>
        </blocks>
        <resources>
            <customclass_setup>
                <setup>
                    <module>Proweb_CustomClass</module>
                    <class>Proweb_CustomClass_Model_Resource_Setup</class>
                </setup>
            </customclass_setup>
        </resources>
    </global>
</config>

app/code/local/Proweb/CustomClass/Block/Adminhtml/Options.php

<?php
    class Proweb_CustomCss_Block_Adminhtml_Option extends Mage_Adminhtml_Block_Catalog_Product_Edit_Tab_Options_Option {

        public function getOptionValues()
        {
            $optionsArr = array_reverse($this->getProduct()->getOptions(), true);

            var_dump($optionsArr); exit;
//        $optionsArr = $this->getProduct()->getOptions();

            if (!$this->_values) {
                $showPrice = $this->getCanReadPrice();
                $values = array();
                $scope = (int) Mage::app()->getStore()->getConfig(Mage_Core_Model_Store::XML_PATH_PRICE_SCOPE);
                foreach ($optionsArr as $option) {
                    /* @var $option Mage_Catalog_Model_Product_Option */

                    $this->setItemCount($option->getOptionId());

                    $value = array();

                    $value['id'] = $option->getOptionId();
                    $value['item_count'] = $this->getItemCount();
                    $value['option_id'] = $option->getOptionId();
                    $value['title'] = $this->escapeHtml($option->getTitle());
                    $value['type'] = $option->getType();
                    $value['is_require'] = $option->getIsRequire();
                    $value['sort_order'] = $option->getSortOrder();
                    $value['custom_class'] = $option->getCustomClass();
                    $value['can_edit_price'] = $this->getCanEditPrice();

                    if ($this->getProduct()->getStoreId() != '0') {
                        $value['checkboxScopeTitle'] = $this->getCheckboxScopeHtml($option->getOptionId(), 'title',
                            is_null($option->getStoreTitle()));
                        $value['scopeTitleDisabled'] = is_null($option->getStoreTitle())?'disabled':null;
                    }

                    if ($option->getGroupByType() == Mage_Catalog_Model_Product_Option::OPTION_GROUP_SELECT) {

//                    $valuesArr = array_reverse($option->getValues(), true);

                        $i = 0;
                        $itemCount = 0;
                        foreach ($option->getValues() as $_value) {
                            /* @var $_value Mage_Catalog_Model_Product_Option_Value */
                            $value['optionValues'][$i] = array(
                                'item_count' => max($itemCount, $_value->getOptionTypeId()),
                                'option_id' => $_value->getOptionId(),
                                'option_type_id' => $_value->getOptionTypeId(),
                                'title' => $this->escapeHtml($_value->getTitle()),
                                'price' => ($showPrice)
                                    ? $this->getPriceValue($_value->getPrice(), $_value->getPriceType()) : '',
                                'price_type' => ($showPrice) ? $_value->getPriceType() : 0,
                                'sku' => $this->escapeHtml($_value->getSku()),
                                'sort_order' => $_value->getSortOrder(),
                                'custom_class' => $this->escapeHtml($_value->getCustomClass())
                            );

                            if ($this->getProduct()->getStoreId() != '0') {
                                $value['optionValues'][$i]['checkboxScopeTitle'] = $this->getCheckboxScopeHtml(
                                    $_value->getOptionId(), 'title', is_null($_value->getStoreTitle()),
                                    $_value->getOptionTypeId());
                                $value['optionValues'][$i]['scopeTitleDisabled'] = is_null($_value->getStoreTitle())
                                    ? 'disabled' : null;
                                if ($scope == Mage_Core_Model_Store::PRICE_SCOPE_WEBSITE) {
                                    $value['optionValues'][$i]['checkboxScopePrice'] = $this->getCheckboxScopeHtml(
                                        $_value->getOptionId(), 'price', is_null($_value->getstorePrice()),
                                        $_value->getOptionTypeId());
                                    $value['optionValues'][$i]['scopePriceDisabled'] = is_null($_value->getStorePrice())
                                        ? 'disabled' : null;
                                }
                            }
                            $i++;
                        }
                    } else {
                        $value['price'] = ($showPrice)
                            ? $this->getPriceValue($option->getPrice(), $option->getPriceType()) : '';
                        $value['price_type'] = $option->getPriceType();
                        $value['sku'] = $this->escapeHtml($option->getSku());
                        $value['custom_class'] = $option->getCustomClass();
                        $value['max_characters'] = $option->getMaxCharacters();
                        $value['file_extension'] = $option->getFileExtension();
                        $value['image_size_x'] = $option->getImageSizeX();
                        $value['image_size_y'] = $option->getImageSizeY();
                        if ($this->getProduct()->getStoreId() != '0' &&
                            $scope == Mage_Core_Model_Store::PRICE_SCOPE_WEBSITE) {
                            $value['checkboxScopePrice'] = $this->getCheckboxScopeHtml($option->getOptionId(),
                                'price', is_null($option->getStorePrice()));
                            $value['scopePriceDisabled'] = is_null($option->getStorePrice())?'disabled':null;
                        }
                    }
                    $values[] = new Varien_Object($value);
                }
                $this->_values = $values;
            }

            return $this->_values;
        }

        public function getCustomCss() {
                var_dump($_POST);
        }
    }


app/code/local/Proweb/CustomClass/Model/Resource/Setup.php
<?php

    class Proweb_CustomClass_Model_Resource_Setup extends Mage_Core_Model_Resource_Setup {

    }

app/code/local/Proweb/CustomClass/sql/customclass_setup/mysql4-install-0.1.0.php

<?php
    $installer = $this;
    $installer->startSetup();
    $installer->run("ALTER TABLE `catalog_product_option` ADD `custom_class` text");
    $installer->endSetup();