You can copy profiles but have to give them unique names, right? Then when you upgrade, just load your old profile. Or am I missing something? Screenscript.lua is CREATED anew from all the Mach4 bits, and isn't to be edited, if I remember correctly.
That said, I like to, when I upgrade Mach4, rename Mach4Hobby to something else, like Mach4Hobby_4162, for example. Than install anew, a NEW Mach4Hobby folder will be created. Then open the old Mach4Hobby folder and the new one side by side and copy your stuff over, plugins, profiles, screens, macros, license, modules. This way you never hose up a good working version. If something goes amiss you don't like, rename a couple folders, Mach4Hobby to Mach4Hobby_Hosed, and Mach4_4162 to Mach4Hobby, and you're back where you started. I never install over the top, NEVER!!