Only top two divisions were required in the end - but you cannot convert back once seating is installed from what I remember.
Reminds me of an AGM in about 94/95.... I argued with Ray Hardman that the Bank should be kept as a terrace, rather than just bolt cheapo seats on. His argument was we're second flight, so just couldn't... my counter, had he looked at the league table recently... we went down.
I'm fairly sure we'd have had more use out of a terrace in the intervening 20 odd years... of which 4 have been second flight.