I have a string like this
\"C://Documents/TestUser/WWW/Help/Files/Move_Help.txt\"
and have to replace Move_Help.txt
There's a one-line solution for this:
rlpStr = StrReverse(Replace(StrReverse(str), StrReverse("Help"), StrReverse("Job"), , 1))
Technically, it's slightly less efficient than combining InStr and Replace but it can be used inside another expression if you need to. Also, I like the one-line solutions so long as they're not incomprehensible.