Please keep in mind that while many of these mid-late 19th century knives can be modified, they are still antiques. Years ago while having this conversation with an old friend he put it this way, "What if someone had modified 18th century antiques for another purpose just because they were plentiful?" It would be a sin to alter a 1740's pistol grip table knife. The day may come when these knives are scarce and valued for what they are."
Just another way to look at things.
Yancey
As I'm sure you realize, they did modify 18th century items for "modern purposes" in the 19th century and then went on to break them or wear them out and finally discard them. Many 18th century guns were "percussioned" in the 19th century and rebored and rerifled or smooth bored and shot until they were mostly or completely worn out. That's why we don't have as many 18th century items as we might otherwise have had.
I'm guilty of having the lenses taken out of an original Ca. 1810 brass frame pair of spectacles and then having modern prescription lenses for me put in them in the 1970's when reproduction spectacles were not available. Yes, I saved the original lenses, but I lost the spectacles during a Battle Reenactment at New Market, VA in the early 80's and though we had over two dozen people looking, we could not find them. (I can imagine some 23rd century Archeologist finding them and saying, "AHA!!! This is PROOF they had prescription lenses in the early 19th century. Grin.)
However, Yancey, I am with you in spirit. With so many good reproductions available, I try not to use original pieces at all anymore or be EXTREMELY careful with them when I do. For example, I needed some "period C clamps" a few times at living histories. I found an original set of four hand forged "quilting clamps" that were just the ticket, but I only use them in good weather. I also occasionally use some 18th and early 19th century pin, hand and bench vises; but don't modify them and use them VERY carefully.
Gus