As long as they are both MB 2.0, there are youtube videos on how to transfer/refresh MB pucks from one band to another. It only requires a screwdriver.
Yes, but you should make sure the puck you insert is listed as active in MDE.
Side note: I've started switching out pucks in my magicbands for more fun color options, like having my Maleficent band with a green puck to match the green flames on the band. The only important part of the MB is the puck and the number on the back, so I go through MDE and deactivate all the pucks except the ones I'm taking on a trip.