I'm curious whether or not this is a procedure that is to be recommended.  I am doing a custom AK-74 project and heard from the builder that he might have to pull the barrel.  What's all involved, and should I be worried at all?

But is it bad to do this over again?  My worry is that the barrel on my SGL was installed by the factory in Izhmash and might not get put back correctly by a third-party builder, or that when it is pressed in the first time, it is somewhat permanent.  Maybe you can clarify the actual process that happens when you install and remove a barrel?

I wouldn't try it repeatedly.  I'm guessing after around 4 passes and you'd need a new barrel or a really snug trunion.  Look in the Builders forum.  Here's a good start for what you wnat to know.

What's involved?

lubricate judiciously with a good penetrating oil (I prefer corrosion x)
press out barrel pin
press barrel out about 1/4 inch
using a dremmel or round file, round over the edges inside the barrel pin cutout to reduce galling on the way out.
clean and lube area again
press barrel out

Should you be worried?

Well that all depends on your builder. I don't consider it a difficult thing to do at all, but many people have managed to screw it up. Put it to ya this way: If your builder has ever referred to your receiver as a lower, run away, far far away