I'm going to test something and I changed the Unregistered ID in usergroup table to 12.
It seems my test worked well, not perfectly as I expected, but it's OK
Thats nice for you, there is nothing physically stopping you from changing any id value in any table, thats not the point. The point is some code is likely to rely on it being 1, so changing it will likely break something - and all for nothing, there is no gain in messing with internal ids, only pain, but if you think you know best, go for it.