This isn't something I'm particularly familiar with so this comment is largely just engagement, but I will say it seems like a lot of icon packs use some kind of template app that they populate with their icons. So the app will be the same but with assets swapped out for the given icon pack. It might be worth looking for some of those templates folks use for publishing icon packs
Maybe someone who knows more about this could chime in with more info
Also worth knowing about if you enjoy customization are kustom live wallpaper (KLWP) and kustom widget (KWGT), which aside from icon packs are often kinda the bread and butter of android theming. Custom launchers are also good to know about, nova launcher seems to be the gold standard to many when it comes to customization features (though they were recently acquired by an analytics company which has raised some eyebrows from privacy focused folks, though I'm not actually aware of any specific problems that have been identified at this point)