Your cabinet, like most, has two JACKS - that makes it easy to connect a second cabinet with a jumper cable from the first cabinet to the second - keeps thing tidier than running 2 cables from the head.
If you connect two amplifiers, you are likely to damage at least one of the amplifiers, maybe both, and possibly even take out the speaker(s) in the cabinet in the ensuing electrical firestorm. It's a VERY bad idea, and none of the equipment manufacturers involved warranties their gear against that. But as specified above, if you decide to do it anyway, film it, and make sure you say "watch this!" before you destroy all your gear in one fell swoop. That way, someone else can earn from your mistake.