If you've got V3, you can take advantage of auto-enumeration, the -Raw switch in Get-Content, and some of the new line contiunation syntax to simply it to this, using the string .replace() method instead of the -replace operator:
(Get-ChildItem "[FILEPATH]" -recurse).FullName |
Foreach-Object {
(Get-Content $_ -Raw).
Replace('abt7d9epp4','w2svuzf54f').
Replace('AccountName=adtestnego','AccountName=zadtestnego').
Replace('AccountKey=eKkij32jGEIYIEqAR5RjkKgf4OTiMO6SAyF68HsR/Zd/KXoKvSdjlUiiWyVV2+OUFOrVsd7jrzhldJPmfBBpQA==','AccountKey=DdOegAhDmLdsou6Ms6nPtP37bdw6EcXucuT47lf9kfClA6PjGTe3CfN+WVBJNWzqcQpWtZf10tgFhKrnN48lXA==') |
Set-Content $_
}
Using the .replace() method uses literal strings for the replaced text argument (not regex), so you don't need to worry about escaping regex metacharacters in the text-to-replace argument.