If I ever did anything like this, it would be done my way.
In other words, I would probably do something similar to adding +8 and nerfing +1-7, and making +8 untradeable and incredibly difficult to get, and +8 is the only part that can be "prestiged". It would create a way to have this "armor customization" without strongly hurting the +7 market, but as a result would be member-only and cap only to the latest sector armour at the time.
+8, of course, probably wouldn't be called +8, but a new type of armour that's "prestigable".