Tiberius gives you one bonus good of an active province.
– take the good and that’s it or
– take the good and flip the 'bonus good' token over?
I am pretty sure it is the first option but I started wondering when I compared it to the "get 1 salt" tile, which is strictly better.
I wouldn't say strictly better. You can't sell salt.
One requires waiting until the good you want is face up, the other can't be sold.