Yeah out of scope, there is a formspec creator thing online for formspec v2, I think by luk3x
In game is 10 times harder, because I can't force you to reload all of the lua files your formspec generation code makes. I.e. you'd have to hot-swap all of your different formspec lua files, and my mod wouldn't know how to do that. Alternatively, I could override minetest.show_formspec(), and save off the past 5-7 formspecs shown to a given player. Then, you can request to see the previous X formspec, and bring up an edit box for it, and also re-render the new version. That might work, but you still later have to go back and change your original code.