What would it take to change the JMS directory from
/multisites
to something more generic like
/sites

When a new customer is set up they get a temporary address during development.
Once their site is ready, then we switch over their DNS.

I'm just wondering if the /multisites directory is hard coded everywhere or is it configurable?

Rename the "multisites" directory into "sites" directory is not easy but you can decided to deploy the slave site into a "sites" directory.

The multisites directory is hardcoded everytwhere and also used by the other extensions like "articles sharing for jms".

If you want deploy the slave site into the "sites" directory, you can etiher enter this path in the JMS slave site "deploy directory" or also use the "alias directory".