I agree with Mary and think that you should have the ability to switch to a reefed main without having to return to your launch area to switch sails. Reinforcing the sail for a new downhaul and outhaul grommet isn't a problem, but can a reefed sail work on my Prindle 18 (all aluminum mast) when it is held up by the rope halyard alone. The other option would be to have a cable made ( and remember to bring it sailing with you) the same length as the reef, with a ring on one end to hook on the top of the mast and the other end fastened to the top of the sail. My concern with that would be getting it unhooked without having to put the boat on its side.
I've seen someone selling an aftermarket ring that has a place to attach a small diameter line that can be pulled from the tramp to unhook the ring from the top of the mast. Maybe this would work?
Here's a photo of a friends Nacra 5.8 with a reefed main.

Jack Hoying
Fort Loramie, Ohio
Prindle 18 #1645
http://www.bright.net/~jmhoying/sailing/prindle.htm