You can, but how would you do it and keep the prop balanced?

They (Dubro for one) makes a weighted prop nut, a rather large brass thing, that replaces the prop nut that is on the engine.

The main issue with those types of weights is that if you should happen to lose one in flight, well, what do you do then? You have a tail heavy aircraft that can be difficult, at best, to land. The other disadvantage is that it puts an undue burden on the crankshaft bearings and bushings which can, eventually, harm them.

The best bet is to move things around as best you can.... move the battery as far forward as possible, mount the engine further forward, and so on, then add the stick-on weights to the firewall to make adjustments to your CG.

CGr.