The key fields on FeatureMerger allow you to use the Text Editor where you have access to all these functions, as well as regex functions. IS this not sufficient?
I guess that is indeed sufficient for the string functions so I removed them from the suggestion.
I am struggling a bit with how to use regex since those functions require a string as input while I would like to use the string entered into the other input (requester / supplier) to be compared against.