Adding a Deterministic variable after sampling

Questions v5
4

Do the new deterministic variables have to be functions of parameter variables or other existing deterministic variables as in this case? In my case, I have a whole chain of derived variables and it’s only the last that I’d like the values for after sampling, akin to:

with pm.Model() as model:
    # priors
    ...
    # derived variables
    ...
    interesting_dv = ... # interesting dv computed from earlier uninteresting vars
    # likelihood
    ...