I just am starting to use this multi-wallet feature. Theoretically, it looks like it will not be that hard. Whenever there's a transaction, I just pre-pend the "-rpcwallet=wallet1.dat" in the command. ie.
bitcoin-cli -rpcwallet=wallet1.dat COMMAND
Let's say I add another wallet in another subdirectory. If I do not add the "-rpcwallet=wallet1.dat" does it default to the base wallet.dat?