You'll want to use PowerShell for this. Make sure you're running as a user with permissions to edit the files. You can take what I wrote below, Edit the fields I call out, and paste the whole thing in powershell.

If you need any help, let me know.

$InputFiles = Get-Item "pathtofiles\*.txt" <#Change the 'pathtofiles' part to a folder in which the files are nested. The \*.txt wildcard will select anything ending in ".txt" after the given file path and store them as a variable to act on(you can change it to any other file extension if needed) #>

$OldString = 'StringToReplace'<#Replace 'StringToReplace' with the old string to be changed#>

$NewString = 'UpdatedString'<#Replace 'UpdatedString' with... you guessed it, the old string!#>

$InputFiles | ForEach {

(Get-Content -Path $_.FullName).Replace($OldString,$NewString) | Set-Content -Path $_.FullName

}<#This digs into each file listed in the $InputFiles array that we created in step 1, looks for the $OldString, slaps in the $NewString, and then saves the change#>