The Theatre stands on a slightly modified 017-1. A ledge that was previously non-accessible can now be reached via a cave that I mapped myself onto an unused corner of the cave map 013-3 (I can move it to a new map, 017-3, if you'd rather - but the space was there). There are two indoor maps, 017-2 for the stage room and 017-backstage for the backstage, but I can combine them if that's better.
Monsters spawning in the cave are Bats, Silkworms and Cave Snakes. On the Ledge I've added a Gamboge Herb spawn in the garden, and some Logheads.
Ledge:

Cave:

Theatre:

Backstage:

The story is that the Troupe Leader in Tulimshar purchased the abandoned theatre and is letting the citizens of Hurnscald perform in it. I've also edited the Troupe Leader's script slightly, so rather than just saying "I'm the leader of a travelling theatre troupe," or whatever, she mentions the theatre as well.
The theatre also uses a couple of new tiles.
Zip file data containing the folders graphics and maps, which contain - respectively - the modified tileset under tiles and the four map files:
http://www.mediafire.com/?mxy0mzzj5md
And the modified NPC script:
http://www.mediafire.com/?mrjnmwmthcm