You can just leave the water as-is with no worries.
As for swapping out with an airlock, that is purely a personal preference. The blow-off tube is technically an airlock, so you are really only deciding if you want to leave it alone with a large airlock or switch it for a small airlock. Either way will work.
Arguing on the internet is like running in the Special Olympics, even if you win you're still retarded.
My internet friends were making fun of my kegdolly and I took it out on Gary. - Ginger