Not yet, but it’s on our to-do list.
That is not supported and not going to be supported. Scopes are all wrong to do that.
If you need varying upper and lower bounds, you have to do it yourself for now, including the Jacobian adjustment.
Even if you’re ultimately interested in the difference, it is usually easier scientifically to model the individuals individually, then derive quantities like differences in abilities to measure.
If you have parameters
alpha2, then you can just define a transformed parameter
delta = alpha2 - alpha.