Close example. Real code that uses stl templates can create much worse cases of compiler reusing functions for template instances.
How i imagine UX. Window for edit calltype have buttons to add extra calltype and delete it. Don’t now how best to show calltypes list for function.
At decompilation stage decompiler make guess by type of function parameters and it 's count, that calltype are appropriate. If guess was wrong, user can chose correct calltype from list similar as it done then choosing union member for variable that have it.