I prefer that people pull the barrel off and send it to me, but I often take apart a whole upper if the customer does not have the tools to do it.
I usually remove the front sight base as well, just makes it easier to hold the barrel through the headstock on the lathe when I re-cut the crown.
If you are considering swapping the front sight base out for a flip-up setup, then it's coming off anyways and that makes it an excellent time to do the swap.
There are a few options out there, ranging from a simple YHM or PRI flip-up front sight base that replaces the standard FSB on the barrel, to a gas block with a picatinny rail that you can add either a flip-up sight or a removable sight tower to.
Lastly, you could go to a quad railed handguard system with a flip-up sight on the rail.
PRI is probably the best flip-up front sight that's barrel mounted, but YHM is half the price and very serviceable.
I think a dedicated barrel mount flip-up is the best option, much better than a railed gas block AND some kind of sight added to the rail.
Some pictures:
YHM flip-up:
PRI flip-up:
YHM gas block mounted flip-up:
YHM gas block mounted tower:
YHM handguard mounted flip-up:
There are LOTS of other options, these pictures were just easy for me to find to show you ideas.