Negate Model Switching - Or Control from System Prompt

I wrote a Sys Prompt recently, and the AI auto-switched to a Pay Per Use model automatically.  (I did not have it set to Automatic.  It was hard set for GLM 4.6) I didn’t realize it till it had already burned through a bunch of my credits!

It would be great if the System Prompt could either prevent switching, prevent switching to paid types, and/or allow the user to dictate which specific models it’s allows to switch to in the course of performing its tasks.