Repaired my heater foam yesterday, took a few hours going slowly and carefully. My few hours of work could have been done in about half that time if I were in a hurry, but I go slow on first repairs to get them right the first time.
I used the technique of removing the radio and front dash console cover, then cutting the vent to gain direct access to the flaps. There is no report of this on these boards, but it can be found by going to the 986Forum website and searching for "Interior vent debris". The 986 Forum says it is a division of Pelican Parts, but I have not been able to access this information from the Pelican Parts site.
The direct link is
Interior vent debris - 986 Forum - for Porsche Boxster & Cayman Owners
It is a five-page report, and I recommend this approach because it does not involve disassembling the heater box, not to mention removing a lot of other parts.
I split the vent at the seams by working two flat blade screwdrivers down them, which separated them to the first riven below the curve of the vent downward. Then used a razor knife to cut the rest of the way. For me, the razor knife made a much better cut than my Dremel.
The two flaps can be moved any way you want by messing with the Climate Control settings.
The remaining foam was removed using a right-angle hose pick, working it around the holes to get the foam off of the backside of the flaps.
I used HVAC aluminum tape, the 1.88 inch wide, and it worked great. Cut strips to size, remove the backing, straighten them out with a little bit of teasing, get a longitudinal curve to retain the straightness and install them.
I then taped the vent back together with Gorilla Tape, made by the Gorilla Glue people.
Good luck to all.