as a professional user I am working full-time on InDesign. In other words, in the past, in forms in A1 and A3 format, double work was done. Because everything that was on the A3 formats had to be on the A1 formats as well. That is a bit of duplication and that is why I am looking for a script that can process all existing forms either of size A1 or of A3 in such a way that all forms can be printed as desired, but that makes the content fluent. Is there such a script?
If you only need prints, what about 2 print presets, one with A3 format, other with A1 ? A script can then be used for printing with both presets or you can use paid-for tools such as https://zevrix.com/ to perform prints automatically.
If on the contrary you need "native" files in form of A1 based on the A3 file, you can have a script to open files in folder, modify pages dimensions and scale contents. But sincerely, as A3 and A1 are homothetic and considering you wouldn't do edits, it might not be worth the effort.