I'm a rookie myself, so take my advice with a grain of salt.
However, I have screwed around with the beer line on a tapped keg, like you are going to do and it is no big deal. You simply have to untap the keg by lifting the handle. I found it easier to pull the release valve first to release the pressure in the keg. Then lift the hand...now you are seperated from the keg. Opening the faucet now should push out the remaining beer in the line, and just replace the line. No big deal.
-Raoul
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