How exactly does salt rotation work? What is the format?

I'm working on an automated deployment script for Mattermost installations, and want to make sure that each installation has its own salt values.

From what docs/comments I've found, the salt is just a 32-char string? In the system console you can regenerate the salt at-will, but what happens if the salt is updated in the config.json between restarts? Is Mattermost able to handle this, or does it do extra work when regenerated via the console?

And all this is also true for the SQL encryption key? How are the previously-encrypted values accessed?

Thanks,
jason.