I'm pretty sure no special handling will be needed in this regard for the latest IotM. I also don't know that splitting up effects and intrinsics would help much, since as far as modifiers are concerned even something like a shirt and an effect with the same name would require special handling.
As for Slicked-Back Do, I think I have some code ready that will distinguish which modifier to apply when you have the effect at least. The best option for not having confusion over acquiring the effect might be to remove that bit from statuseffects.txt. Actually, hair oil is listed for both effects there, but I doubt removing it from the second one will fix anything on its own.