I purchased the Delta Pack and was curious if I could unlock all the Tier 6 ship traits but also discharge the ships. I'm forced to do that since I only have 1 empty ship slot.
Apparently the game saves your progress on T6 ships. So if you discharge it and then get the same ship again, you'll still have all the levels you unlocked for it. This is probably why the trait stays unlocked.
So have no fear if you want to discharge your T6 ship! Discharge it and know that your hard work is safe.