I've written the GIMP Script-Fu scripts. I've written the PowerShell wrapper. However, I can't get PowerShell to properly pass the parameters when GIMP is invoked.

If you find the text looks changed when the file is downloaded onto a Windows host, you can create a duplicate copy of the text using the Out-File PowerShell command using the Encoding parameter.

Whether the string you're looking for inside a text file is a single word or a complicated pattern, PowerShell has the ability to find and replace just about anything.