Mainly just curious, but how is headspace reduced on a rimmed action? Is this ever a problem aside from a double being off the face?

I can not see how a double rifle can be rebreeched to reduce headspace.

The headspace is determined by the rim thickness on a rimed case.
The hinge pin is replaced or welded up and refitted.

All that will do is bring it "back to the face". If the headspace is off, this may or may not fix it. It may have started out with excessive h'space originally, however I doubt it. If that be the case, there is not much one can do.

As others have said---If the chambers were reamed too deep to begin with they need to be replaced.

If it's off the face there's several ways to repair it depending on how it was made to begin with and what type locking system it has.

couldnt you rebore the hinge pin location with a larger pin, moving the whole assembly back towards the breach face, and then face the breech end of the barrel to cut down on the excessive headspace?, the kicker will most likely be, what kind of action it is?, and how many lockup spots there are......still thinking you can do lots of work that will be cheaper than replacing the barrels!!!!!!!bob

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The point is this: If the headspace is excessive, and the barrels are on the face, it means the gun was a cheap, ill-made, and possibly dangerous POS to start with. It's not worth fixing.