If I have a custody order set in one county, can I file for a revision or a new order in a different county since I live in a different one now?

The county where you have a custody order retains jurisdiction.  If neither parent lives in the original county, then you have grounds to file a "motion to change venue"--asking the court to move the matter to your new county.  You would use a request for order (FL-300) and request other relief being "change of venue."  See Code of Civil Procedure § 397.5 If you don't want to deal with all of that--then simply file in your old county.