At the expense of sounding like a wise ass; Is the Pope a Catholic? There are several AS sponsors who do saw mods, as well as several members who mod their saws. There are many opinions on this site concerning all of the above. Hopefully, you will receive some private messages (PM) that give you some insight on personal experiences to follow or avoid. Treat them respectfully and with confidentiality and you will soon become a respected member of this forum.
Having said that, yes you can do the obvious muffler mods, do a 'Search' of that subject and you will get enough reading and pictures to last you for a while. It's a no brainer, if you have a torque wrench and a hand held drill. The 026/260 series and the 036/360 series Stihl chainsaws all respond well to a simple muffler modification.
Modifications 'beyond' the simple muffler mods, require knowledge of 2 cycle engines, tools, expertise and common sense -- not all of which are possessed by the average chainsaw owner, so seek a pro to do it right. Cost for a 'woods' saw mod will be about $200 and includes return postage of the saw. That will be a mod that enhances its performance as a work saw.
Further mods to make them into a competition and race saw can be very expensive and requires even more care in the selection of the 'expert' to do the mods. And get a grip on your billfold, because this may not be cheap.
Hope this helps.
Tom