void Main()
{
    string s="indicator[0].radicetion[0].kodsad";
    int[] replace={1,3};
    int i=0;
    s=Regex.Replace(s,@"(?<=\[)\d+(?=\])",m=>replace[i++].ToString());
    Console.WriteLine(s);  //indicator[1].radicetion[3].kodsad
}