This a pet peeve of mine, but the way the current ship names are assigned doesn't work well with numbered classes. For example when you design a V1-class DD as Germany, it can have ships in it that are named with different inital letters like G-43 or Z-86. I think it would clear up some confusion if auto-assigned ship names would have to start with the same inital letter as their class.
The historical Imperial German Navy assigned prefix letters by constructing shipyard, not by class, and there are multiple examples where two or more prefix letters were used within a single class of destroyer / large torpedo boat. I would therefore suggest that it is very unlikely that this will be changed.
If you want to have a class-based naming convention, or use a single letter prefix for all of your destroyers, then I would suggest going into the ship names file, removing all of the destroyer names, and just using the prefix letter.