Installing Multi DB after having already installed Supporter Plugins

In the supporter documentation it says:

If you are using Multi-DB:

* You need to add the global table lines to db-config.php BEFORE installing the Supporter plugin or running the sql.txt
* Add these lines to your db-config.php if using multi-db:


* If the auto-install does not add/modify the db table(s) for you once you've installed the Supporter plugin then run the sql code in "upgrade_sql.txt" on your wpmu db

What happens if you already have Supporter installed and you want to THEN install MultiDB??

Will it kill my site? Has anyone tried?