Access Tunnel

• WWizards of the Coast2021-04-16
  Official Ruling
  Once a creature with power 3 or less has been blocked, Access Tunnel's second ability won't cause it to become unblocked.
• WWizards of the Coast2021-04-16
  Official Ruling
  If the target creature's power is greater than 3 as Access Tunnel's second ability tries to resolve, the ability doesn't resolve. However, if instead the creature's power is raised above 3 after the ability resolves, it still can't be blocked that turn.

Rulings via Scryfall