Hi Gunnar,
You cannot convert an assembly cut into a part cut, but you can see an assembly cut into a part. Follow me:
(Pro/ENGINEER 2000i)
Go to your assembly and redefine your cut. Choose INTERSECT PARTS->DEFINE->now from INTRSC OPER choose REMOVE MODEL->ALL->CONFIRM.
Now choose VIS LEVEL->PART->DONE->ADD MODEL->choose your part->DONE SEL->DONE->OK
It's important to remove all intersection done by the assembly cut and then to select the visibility level and at the end to select the part you need to intersect. If yu try to redifine the VISIBILITY LEVEL without removing the parts, Pro/E will not show the modification. I don't know if is a bug or not, but for sure will give you a headache.
Now, if you load the part intersected by the assembly cut, you will see the cut in your part.
Be careful if you assembled this part in several places! Now, The part has the cut!
... and there is a link now between your assembly and the part.
Good luck
-Hora.