AT2 does not manage SID, not right now.
I don't understand what you are trying to achieve, though. There are many ways to produce SIDs, even on a AY/YM, but are you talking about that kind of SID? "sid registers" does not really mean anything. So maybe what I'll talk about here is off topic.
One thing you can do is explore the YM format by Leonard and see how SID is encoded, but the format will only give you hints about what timer to use. Then it is up to YOU to chop real-time the square envelope, via volume or the mixer (already two ways of doing SID), according to the period of the notes being played. Doing it on CPC+ helps, thanks to the timer (Offset has already an available player, one of the latest demo on CPC+ uses it... 15 years after Offset release his player (which shows how much SID raises interest...)).
On CPC old, BSC did another kind of SID, called SID-sample. Tiny samples are played. Make a search on the forum to get it. Once again, no one was really interested, sadly for BSC...
So the SID question is vast, highly technical, and basically, if you don't master assembly (and have a good ear), you won't be able to do much!