Strange that some people will advocate breaking the rules rather than finding out the true position which is actually very simple.
You need to contact the DGAC for permission to operate an aircraft which does not display its civil markings (which is the actual issue, rather than the "military" aspect).
This permission comes free, and is turned around quickly. The friendly and helpful chap you need to contact is Philippe Auradé who can be reached on:
[email protected]
Tel: +33 1 58 09 42 98
Fax: +33 1 58 09 43 47
He also deals with the related issue of approving non PFA Permit aircraft to fly in France.
2D