This follows on from
Using the standard Moodle editing interface, you can only set certain values for pagetypepatterns for blocks. This is all that most people will want.
However, the underlying blocks system is capable of being much more flexible that that. Do we want to support power-admins who want to do weird things by, for example, putting custom values directly in the blocks table.
All I propose we do is what is already suggested in a comment in the code:
I suggest that we do actually add the custom page-type to the menu, with a clear lang string like "Special non-standard value 'mod-pony-*-foal'".