package main

import (
    "math/rand"
    "fmt"
    "os"
    "strings"
    "time"
)

func modifyString(str string) string {
    if len(str) < 10 {
        return str
    }

    rSrc := rand.NewSource(time.Now().UnixNano())
    rg := rand.New(rSrc)
    runes := []rune(str)

    return string(runes[rg.Intn(len(runes) - 1)]);
}