Straightforward enough I think.
You are required to work to the most restrictive of your licence / CofA privileges and local regulations. If you are requested by ATC to do something you can't do, you decline (giving reasons why if this is practical) and either ask for, or offer, and alternative.
If flying as PiC in another country you have a legal duty to know what rules apply to you. On long GA trips, this can be a major faff, but you still have to do it.
G