<ports>
  <op_var_tank label="Tank Port">41502</op_var_tank>
  <pls_vimvom label="Local Port">61160</pls_vimvom>
</ports>

sed -i -e '/<ports>/,/</ports>/ s|Port">[0-9a-z.]{1,}</|Port">1234567</|g' text2.xml

Port">

</