Range rules trump USPSA rules, but this can get sticky and is best worked out beforehand.
If a range/club wants to shoot USPSA they, for the most part, need to be willing to adhere to the ruleset.
3.3 Applicability of rules
USPSA matches are governed by the rules applicable to the discipline. Host organizations may not enforce local rules except to comply with legislation or legal precedent in the applicable jurisdiction. Any voluntarily adopted rules that are not in compliance with these rules must not be applied to USPSA matches without the express written consent of the President of USPSA. All local rules allowed under these provisions will be documented at USPSA HQ.
A. Is it frowned upon to go up to the safe table with loaded magazines IN you're belt? I never really asked. I just suspect its no big deal.
Some prefer to go to the safe table without mags in their belt to avoid inadvertent handling. Like maybe thinking they had emptied their mag to dryfire, and then realizing they hadn't - or something like that.