My thoughts, and I absolutely mean no disrespect and I think others will agree with me, is that, with the questions you are asking, whether you should even be attempting this task. You absolutely need to disassemble everything first. You can't just go cutting through a compressed spring (extremely dangerous) and a strut housing with a strut cartridge inside of it. And, sooner or later, you will need to remove the gland nut to insert a new strut cartridge to replace the one you cut in half with a new, shorter one.
Mike Milesk
Tucson, AZ