Me and my mac key

Does that sound like the start of a really old song or what...

Any way on a slightly more serious note-:

Currently in mid migration and my question is
Are mac keys a once in a lifetime thing.

Is my mac key going to be the same if i wanted to move again in 3 to 4
months, or have i to request, what will be a different numbered key,
next time round . 'Should the need arise'.

A MAC is valid for the current ISP you are with, and only for 30 days
from the date it was generated. Your new ISP must submit the MAC to BTw
within those 30 days in order for it to be accepted. If you miss this
deadline, then you would have to get another MAC from your ISP.