On the MB folks try any way to re-use a well loved mat.
I do not reglue the mat - I just use Painters Blue Tape. You know the kind for walls- and you want to tape off the area..... Works great and this is how I do it:Here is the cut I did. Cut the card perfectly.Here is if I wanted to use a middle of a sheet in the middle of the mat.
I have two mats. and I always keep some pieces on the side until I am ready to cut.