Yes, it is a big deal since the WHOLE DB Connection string is associated with each project AND is used when your QC server starts up.

Tell your users that your QC instance will be offline for awhile during this change.

This will be a bit tricky as you need to stop the HP Application Lifecycle Management service, THEN have your DBA change the port and tell you what it is.
Then you need to change the connection string in the siteadmin.xml file (per linked articles below), and start the HP Application Lifecycle Management service.

Now, in Site Admin, you may or may not have a NEW additional DB server on your DB servers tab, look for one with the new port. If you do not have it automatically created, the easiest thing to do would be to create a ''NEW'' DB server in your DB server tab with a different short name than your original one and use the NEW port there.

Take note of the new DB Server's name from the DB Server tab AND of the new DB connection String/URL.

Use that information to alter your project DBID.xml files later when you follow the Remove/Edit DBID/Restore process outlined in the linked articles below.

Changing DB Server:
http://eyeontesting.com/questions/8824/how-to-get-our-existing-qc-server-to-use-a-new-dat.html

Changing hostname:
http://eyeontesting.com/questions/5714/how-do-we-change-the-alm-designated-db-server-from.html