No, it's not. once a model is initialized the "rules" are:
 - model.param_names cannot be changed.
- the value of model.parameters can be changed but not the size, this change triggers a change in the individual parameters
- model.par1, par2 ,i.e. individual parameters can be updated (by a user) and this changes model.parameters.
- param_dim cannot be changed after initialization
- param_sets cannot be changed, they are always constructed from the current individual parameters.
Basically the goal is to keep individual parameters, model.parameters and model.parm_sets always in sync. 
I think these are all parameter relationships. There are a number of places where errors like this are raised because any time a parameter is updated its shape is checked.