Have you seen any studies showing long term corrections to the transport system after mega dosing thiamin?
This kinda reminds me of the ketotifen vs enzymes study and how in the long run you're likely better off tanking your histamine levels for a bit to help the pancreas regenerate. Every bout of high dose cypro and other metabolic boosters seem to restore my ability to function at a high level without supplements
Have not seen studies on improved transport system from megatherapy, but like you said, that may be corrected by an antihistamine or anti-serotonin agent. Niacinamide seems to actually be a diseases-modifying agent for many autoimmune conditions (likely by raising NAD) so it may be something worth trying considering the comments by GorillaHead above.