For icons in many cases hoi4 prepends things like GFX_decision_ before an entered icon name (and doesn't it if it already has that prepended) in the case of decisions
So in maybe an option like affix[prefix,<type>] or something like that would be helpful?
So in the case of the example it would look like this.

 icon = prefix[GFX_decision_,<spriteType>]

so if in the game files it would say icon = generic_decision it would look up the GFX_decision_generic_decision instead of generic_decision

Edit: on a related thing. Icons for focus also automatically looks for the icon appended with _shine so also some way of double checking a type without an affix and with an affix

Also for ideas (national spirits, designers,etc.) by default without setting an icon will look for the ID of the idea with the GFX_idea_ prefix for an icon so a way of allowing you to check that a type is also in a different type would be helpful (with and without affixes)