For a discussion of this very subject (customizing and installing infinite rooms) and a solution you can explicitly use in your case you can look at the following (read to the end of the thread):
"Customizing and hot-swapping room data"
You'll probably have to experiment a little bit - be sure to backup your critical room data and use test data until you understand how magic numbers work.
Maybe starting a separate new subject/discussion-thread
"Customizing, Saving and Restoring Room Descriptions", a title that makes more sense than "Freezing Rooms" or "Only show instance 'squares' when usefull" would be helpful for anyone else in the future searching for info, about customizing and randomly loading room descriptions?
Share what you learn as you solve your problem - would be the sporting thing to do.
Sven
p.s. Thanks Zig and Masterchief...