@Patrick1 I have read the RE-D directive and I don't see the requirement to test (re-test) your whole product except if your product contains a new radio emitting device or changes to the antenna. The EU RE-D Q&A - states "any other radio equipment that was already placed on the market before 12 June 2017 will continue to be sold, provided they comply with the legislation applicable at that time". Since the photon (with or without headers) conforms to and has been sold since before 12 June 2017 with CE mark. The integration documents from Particle are clear on this as well.
For the Photon/PØ and P1 Modules, these integration instructions are the same as for the FCC/IC--so long as you're integrating the modules without modifying the RF design or implementing an antenna with gain greater than that used in certification, your equipment will likely remain compliant.
I am working with a customer to bring a new product to market but with a photon at its core. Our assumption is as above and our focus on testing is for EMC EN-55022 with things like suppression of switched power supplies.
I would appreciate if anyone in the EU countries believes this view is incorrect.