I totally agree regarding the egr, I have to mention the legality side as a matter of course as a moderator. At this moment in time the MOT only checks it's fitted not that a cheat device has been fitted to the ECU. The dvsa are talking about changing this my checking the ECU every time a car is MOT'd however, with how long the dvsa take to do anything it'll be mid 2030 by then.
I fully understand why you're looking at taking the route you are. And if it passes emissions then happy days.
The only way you'd ever come unstuck is if you had a crash and insurance company checked the ECU.
Sorry to hear you had such a bad experience on the a2 forum. Hope you're experience here is better.
Regarding swirlflaps I know the 3.0tdi suffered from.issues either them and owners resorted to deleting them.