The word was changed to beren in the Etymologies, but meren would be restored together with mereth
Noldorin
mereth
noun. feast, festival
bereth
noun. feast, festival
mereth aderthad
proper name. Feast of (Games and) Reuniting
merethrond
proper name. Great Hall of Feasts
meren
adjective. festive, gay, joyous
The word was changed to bereth in the Etymologies, but was never changed in the texts (cf. Mereth Aderthad and the compound Merethrond)