I have been trying to learn about Regular Expressions and have to admit that I find it difficult.
Using various bits and pieces I am trying to sort out McX
RE: Mc Words.
Field: Tag
Regular Expression: \bMc(?=.)
Replace Matches with: Mc$upper($1)
I gave you three different examples to try out.
At first, you should try to follow the examples, they work.
If you have success, then use an example with your values.