Yes you can but as a matter of courtesy I would let your consultant know that you are changing. It will also mean that she idn't chasing you up and pestering you to come back to class!
I change frequently to get new ideas, never has been a problem unless you have a holiday week and the machines don't tally and they try to charge you for a missed week x
Yes you can attend any group as you are a meber of slimming world not just the group you registered at
I'm thinking about doing what Rosie says about changing groups just to get fresh idea's etc