Unfortunately, to make Mac OS support I need a Mac computer, if you have a GMS2 desktop license you can build it by yourself.
You can change the shift key to another in GMS2 object0 ->Step event-> line 53-> replace 'keyboard_check_released(vk_shift)' to ' keyboard_check_released(ord("F")) ' you can write any char instead ' F '
Do you need to scale the whole weapon or delete big parts from the generator?
You can delete parts by deleting frames in parts sprites but do not forget to delete the same frame in mask sprite for the same part.
If you need to scale the whole weapon it is problem because you need to redraw all parts.