No matter what you do, there will be differences between fish bred in the wild, and those bred in captivity. It is unavoidable. Your method of not interbreeding will NOT lead to the complete preservation of the the species traits you desire to achieve. You... are only dealing with the appearances of the fish, not the total fish. A fish (or any living creature for that matter) is far, far more than its "Appearances". Just because it LOOKS right doesn't mean it ACTS right. That's why I said that what you are attempting to do is impossible. You may be able to keep them LOOKING correct, but what about the subtleness of behavior, attitude, etc.? Guaranteed... your correct LOOKING peacock will stick out like a sore thumb to a real, wild peacock if placed in the wild after spending a couple of years in your tank, maybe not by looks, but by the simple fact that YOUR peacock expects to be fed. So hence... you are changing the species anyway, if not by looks, then by other means.
Thats just my opinion though... I could be wrong.