Can I put a 22 inch bar on my Stihl MS250? I am not a heavy user, but I do need to cut logs, along their length, and need more than 18 inches...
You can (I'm assuming you can find a 22" bar that will fit that saw), but it will be slow cutting. And I mean slow. Ripping a log is slow work in itself. Most do this kind of thing with 80cc+ size saws. I did it once with a 65cc saw and it took awhile.
If you really need to do it, I'd recommend buying a ripping chain to go with the bar.
The 230 and 250 use a unique mount, as far as I know 20" is the longest available. As masiman suggests, it is going to be a long day trying to rip with that pup. Oregon makes a ripping chain, 95R, that will fit but don't expect miracles.