Aye, traditions should be allowed to evolve, and I applaud both the "Greenface" suggestion and the idea of seizing the "teachable moment" to help an audience understand that blackface (at least in some traditions) was merely the lowest-budget disguise available to many working-class/peasant mummers.

The central tension of many Mummers' Plays, the "archetypical battle" of a British Hero and a Turkish Knight, is another item ripe for good-natured tweaking and worthy of ongoing research & debate.
Two years ago, our local (Maine, USA) play included "Sir George of Texas" and a Turkish Knight-type character who sang little ditties like "Osama-enchanted evening..." Bad puns flew thick and fast, and every character was made to look equally silly in the eyes of the audience. The "quack doctor" figure--the one who typically raises the fallen fighters back to life at play's end-- treated them like naughty children who had forgotten their better natures, and reminded the audience (in rhymed couplets, of course) that education & understanding are the best medicines for the illness of war-mongering. The play was grand fun and well-received by a politically diverse audience.

It is their ability to bring social mores and inequities into the limelight that makes Mummers' Plays so vital & dynamic. (Hmmm, "limelight..." Maybe that's another good reason to opt for Greenface?) While other folk performance forms such as Morris Dancing may lack the "message" aspect of the plays, there may still be ways to playfully finesse or interpret the use of blackface and other "questionable" aspects & symbols--for example, a jester/joker/makeroom character can interrupt and play "professor" for a minute, with enough humour to hold & keep the audience.

We've used the Mummers' Play format to address all sorts of local political & social issues, all while maintaining a traditional form and (mostly) traditional dialogue, gleaned from scripts in the aforementioned Folk Play Research website. Rather than getting upset & feshing ourselves about clueless onlookers and "troublemakers" who don't understand the tradition, let's continue to have fun with the genre and its creative possibilities!

--Cuilionn