My friend told me that there have been a few ocasions when a customs official in a foreign country requested to open my friends tefillin because he had never seen anything like this before and suspected that my friend might be hiding drugs in the "black box". My friend refused and was asked harsh questions until, eventually the customs official relented and released him with a harsh warning.
Customs officials are usually non-Jews, and we can assume that while they will find a way to open the box, they won't put it back together. Can someone nonetheless allow customs to open the boxes and even unroll the parchment and do what they want with it, or is there some point when one should protest at the beginning? What if you're concerned that the official may inadvertently damage your tefillin in the process?