Default [Q] SIM Card Dual Swap

I have searched the forums and found one thing close but not actually this so I'll ask.
Lets say I have two phones. One uses a micro sim and the other a mini sim. Can I insert both with the same number and use them one by one (use one then turn wireless communications off, and turn the other one on)?
I read that if the network sees two IMEIs on the same number it will disable the actual card.
I also read that if you request a new SIM the old one becomes useless when the new one is actually registered but, there is a way to have "SIM swapping" with two cards. So back to my question with the inserting both, can I request a new card (I have a micro sim now and need a mini sim) and safely use it for "SIM swapping" (having both sims in a phone at the same time.) without disabling the old card.

Sorry if that didn't make sense.
Thanks for any help
FastJelly Android 4.2.2
I'm not a true developer just a newbie trying to code. If anything goes wrong shoot me a message and I will help you fix whatever is wrong. (Just don't actually, you know, shoot me.)