National procedures will differ. However, this is the recommendation from ICAO 9433, "Manual concerning Interception of Civil Aircraft" (basically, turn off Mode C/S to avoid RA):
If the intercepted aircraft is so equipped, the ACAS may perceive the interceptor
as a collision threat and thus provide a resolution advisory for avoidance.
Therefore, care must be taken that such an avoidance manoeuvre(s), if undertaken
before the pilot-in-command of the intercepted aircraft is aware of the interception,
is not misinterpreted as an indication of unfriendly intentions.
This situation can be avoided if the interceptor suppresses the transmission
of pressure-altitude information in its SSR transponder replies within a range
of at least 20 NM (approximately 30 seconds) of the aircraft being intercepted.
This prevents the ACAS in the intercepted aircraft from using resolution advisories
in respect of the interceptor, while the ACAS traffic advisory information will remain
available.