sourcing external read-only constraints files from within the QSF file

Also note that I have seen designers do full Tcl scripts to build their project. If I remember correctly, they basically removed the project and then re-built it out of their Tcl files, all using Quartus Tcl interface. The benefit is that they have complete control over their source .tcl files, and Quartus will never modify them. The downside is if you use the GUI to make assignments, you then need to "capture those assignments" and add them to your source Tcl files. Perhaps you could do some sort of combination, but it's not ideal.