Today I was looking for a way to get the last character of a pattern so that I could replace it. In this example, I wanted to find the last pipe in a record like 8|34346|. Normally with regex, one could do this using a lookbehind assertion. To do this with notepad++ you must utilize the implicit search buffer, by using a \1 in the replace field (for example, to access the first set in the buffer).
So by searching on: email@example.com|lastname,first name|X
"Find What:" ([0-9]*[|][0-9]*)[|]
"Replace With:" \1%
I could get: firstname.lastname@example.org|lastname,first name|X
BIG THANKS TO DEAN NAIRN!