You can’t do that. This is because of a Rhino bug that has been reported but completely ignored by McNeel. Anything you add after the RunPythonScript will execute before the script starts and that is pretty useless.
This is all explained here in the original Filleting Tangent Surfaces discussion.
The solution to the problem is to add the macros inside the python code. This is the python script that does that: Filsrf_crvs2.py (41.3 KB)
If you open the script in python editor and go down to the end of the code, you will see the macros that have been added to create the joined edge curves and joined fillet string.
Joining the fillet string is undoable. It takes 2 undos to completely undo the script.
Also the edge curves are named so you can have the following macro before the script to clean up all the extra bits made when the script created the previous fillet string:
noecho ! selnone
-selname “check” pause delete
-selname “sidecrv*” pause delete
-selname “trimcrv*” pause delete