Code:
plain_nnedi = core.nnedi3.nnedi3
core.nnedi3.nnedi3 = core.nnedi3cl.NNEDI3CL
If these were regular Python functions this would work just fine, but idk about VS' Cython modules - try it and see. It should work though - you can assign to (and overwrite) builtin standard library functions in Python if you want.