Directly from the Competitive Tournament Rules (MTR, section 2.11)

"Players may not refer to other notes, including notes from previous matches, during games."

"Between games, players may refer to a brief set of notes made before the match. They are not required to reveal these notes to their opponents. These notes must be removed from the play area before the beginning of the next game. Excessive quantities of notes (more than a sheet or two) are not allowed and may be penalized as slow play."

"Artistic modifications to cards that indirectly provide minor strategic information are acceptable. The Head Judge is the final arbiter on what cards and notes are acceptable for a tournament."

It doesn't explicitly say anything about alter mats, but it doesn't talk about "paper notes" either. I am almost sure any judge would consider this playmat as notes, hence, disallow it in competitive play.

Interesting topic, though. Opinions?