My question is two fold. First, can you install a set of Briley 20ga tubes into a damascus barrel. And two, is that looked upon as sacrilege?
The answer to the first part of your question is, yes, full length tubes can be inserted into damascus barrels and I know this is a service Briley offers. The concept is generally referred to as Chamber Sleeving, and it generally requires a drop in one gauge - 10bore to 12bore, 12bore to 16bore, 16bore to 20bore, etc.
The second part of your question will be met with a wide berth of opinions. I think from a collector perspective, you'd be devaluing the gun. From a usability standpoint, you'd be making a, maybe, unshootable gun functional again, so that's a good thing. You have to factor in what the weight of the tubes does to the handling of the gun and such, but you could end up with a real pretty gun that's fully functional - and in the process, you'd save another piece of history. Not too much of a sacrilege in my book.