Customizing Revisions with a 3rd different

Hi guys I have a issue with revision codes I only have either numeric or alphanumeric options which is only 2 to have on my sheets however I need to add a 3rd one now due to client request as you can see on the sheets I only have P01 C01 as the proper way of doing it however I used text as a B01 which is not correct way of doing things

What if you split the value in two parts
1 a prefix
2 the value