A non central parametrization would just be pm.logp(pm.Normal.dist(0, 1), theta) And then you separately define a new theta as new_theta = theta * 2 + 4 and use that wherever you want.
.dist() is not a draw (at least in this context). It’s just an object representing a specific distribution. As an input to logp, it specifies what density should be returned.
Having shown all this in the thread I would still suggest trying to use PyMC as it’s intended, that is specifying a random generating graph and not thinking about the density side of it