At this point, COMAC should forget about gaining certifications from FAA and EASA for their C919 altogether. Neither the US nor the EU are ever willing to see COMAC challenge their darlings, Boeing and Airbus. They would rather block access and sales (the US) or drag out the certification for as long as possible (the EU) just to make COMAC's life as insufferable as possible, perhaps even "better" by forcing COMAC to kill the C919 and abandon any future airliner projects that posses even the slightest threats against their duopoly.
Hence, trying to use any foreign-based/sourced components in the C919 in exchange for their certification is rather moot at this point. China better get going with efforts on full localizing of their aviation sector as much and as effectively as possible.
Yes, I'm sounding very pessimistic, but that's how things are. Though I'm not sure whether there are people in COMAC, AECC and CAAC who still refuse to acknowledge reality...
Come on, Beijing! Sometimes, what people do lack are some canings!