If you have the nerve and a steady hand, you can do some work on the sleeve, case, and crank, and clean up the sharp edges...it will help the efficiency but you're not going to get a ton of perf. increase...maybe a few hundered r.p.m. I've done it many times, and have a routine that works for me...but it took practice and botching a few emgines in my early attempts. I can see gains of perhaps 500 r.p.m. without loosing tractability.

The above mods will be more effective if you have a good exhaust system...and a carb that will let the engine breathe well, without being too big.

The thing is...you don't get something for nothing...if you want substantially more power that means working so the engine puts out more power at high r.p.m. usually meaning you loose a little tractability at lower r.p.m. and perhaps the transition through the mid range if you really "have at it"...so...what it all boils down to is, what do you want/need the engine to do for you?

If you want to learn, get a few old engines that aren't of any great collectable value, and try it yourself..."experience is the best teacher" as they say...don't be afraid...just try it and see what happens. If you try something and it works, great! If it doesn't work...don't do that again

Maybe find an old Magnum .40 or a K&B .40 or .61 or something along those lines, and experiment.

Some relatively simple things you can do are to put a radius on the lower edge of the I. ports in the sleeve...if you have any questions as to which ones they are, just look at the sleeve of a typical .46 two stroke for example...the I. "boost" port is directly across from the exhaust port. The ports to clean up are the ones that are 90 degrees to the boost and exh. ports and are directly behind the carb, and right above the backplate. Just radius the lower edge or chamfer them similar to the lower edge of the boost port. Do not get carried away, and do not go into the inside of the sleeve...

You can do a little blending on the crank, by putting a radius on the rear inside edge of the induction window, and a radius at the rear of the intake passage where it opens into the case. (don't nick the crank-pin ...put a piece of brass tubing over it to protect it )

Some engines are nice and clean inside...the castings are well finished, and the port passages match the port openings in the sleeve. Some are rather crude though, and you can port match the case to the sleeve. The exh. manifold or muffler flange to the case can be matched if necessary...the area under the carb can be worked a little if necessary, etc. etc. etc.

You will need several (different shaped ) Tungsten Carbide cutting "burrs" (1/8" shank ) like a straight, and a flame shaped, and a ball end will work for starters, and a variable speed Dremel...eye protection of course...gloves, a good light source...good eyes and a steady hand, and the testicular fortitude to allow you to start cutting / removing metal on a perfectly good engine!

Some will tell you to just get a bigger engine...that's the easy way...(maybe a bigger/heavier engine is out of the question though? )
I like to fiddle with stuff...and if I can make an engine run stronger...(and I can ) then to me, that's just another aspect of our hobby.