Yes it will be quite obvious, the MOMO knob is round and the stick of the box is rectangular so you will just round off the four corners a bit at a time till it fits.
Took me maybe 10-15 minutes with a dremel, make sure to wear gloves as it will get hot, also I did not do this while in the car, I had removed it as I was installing a short shift kit at the same time.
There is a write up on Pelican Parts.
Pelican Technical Article: Boxster Gear Shift Knob Replacement and Upgrade - 986 / 987