You could get someone to code You a small .exe that can be called from a batch-file, answering to/acting on parameters.
Say You have something like "replace.exe", then You could call in normal fashion:
"C:\>replace /with:ascii20" or just put that in a batch-file.
The .exe could be a bit more advanced; feed it with a textfile of characters to
look for as one parameter and then the character to replace them with as another parameter.
