Is it possible to change single player rules at all, to make it more like some of the multiplayer servers? for example to make it step 20 or 40 frames between turns or to disable limb removal or enable disqualifications?

Well, far as I know, bits are answered in some thread, others in another etc, often as not off-topic, maybe making it a bit hard to track down. So:

Grab a replay in Toribash's 'replay'-folder and open it in notepad or some such .

Fifth line'll say something like:

NEWGAME 0; 500 10 0 0 0 2

I'm guessing the '0' before the semicolon means it's a singleplayer game (while 1 means multiplayer). '500' is the match length, and '10' the "turn" length. I've no clue what the next three zeroes mean. The '2' at the end there'd be the rules used:

0=DQ and decaps is disabled
1=DQ is enabled
2=Decaps is enabled
3=Decaps and DQ is enabled

Mess around with things, save the file, open it in Toribash and press 'e' for editing it to play with the new settings.