I wrote a script that translates ES Modules to legacy imports syntax
It allows me to generate an extension package that support pre-45 GNOME Shell versions from the code for GNOME 45 and later. Of course, just rewriting imports/exports is not enough, I also have to post-process the code a bit with sed. But imports are the main part.
Just for the information for the people who may want to keep support of older GNOME versions in their extensions too.