You can pass arrays for inputs. Let’s say you wanted a vector of 10 normals, all with unit standard deviation, except the last one which should have half of it.
import numpy as np
import pymc as pm
with pm.Model() as m:
sigmas = np.ones(10)
sigmas[-1] = 0.5
x = pm.Normal("x", sigma=sigmas)
...
Does this answer your question?