Are we sure Portrush would be a custodian? There sure were a lot of alterations for this Open, including the wipeout of two original (albeit weak) holes on the Dunluce and the wipeout of two good holes on the Valley. On the other hand, there's probably great things about the CLUB to consider.
And I guess plenty of the 147 Custodians have altered plenty of things... so maybe. But Portrush wouldn't necessarily be "automatic", IMO.