Filter-mark specific duplicates

I have quite a number of duplicate files.
MD5 wise they are duplicate, but not the files.

I'd like to mark specific files, namely with specific text in the filename.

for example
some duplicates start with x_ or end with _th

in find duplicates with 'Delete mode' enabled many times the wrong files are selected.
setting a filter isn't really a solution as the initially marked duplicate isn't clear.

Any suggestions?