you are a dumb-ass. AGENTS stationed in ANY foreign country, are technically ASSIGNED to the local EMBASSY as their BASE OF OPERATIONS. As such, they are, by premise; members of the local Ambassador's Security Team, and being members of a diplomatic security team, are entitled to to Diplomatic immunity. As such, Agents can shoot anyone, anywhere (provided probable cause to avoid international incident) and not be charged.
ERGO, Mexico, has NO AUTHORITY, to deny ANY AGENT IN COUNTRY the rite to bear arms, or by any means, defend themselves with the use of deadly force.
your argument is invalid.