Tuning Possible to "tune" old west revolver replicas?

Sure, but the idea is that it might result in a gun worth having done it.

My concern is more that it's just not achievable with modification effort--it might require pretty much machining a different device. As such it's a whole different kind of task. 

For example, how much muzzle velocity can be gotten with only 7 inches of acceleration? I suspect not much more with the power plant used. 

Well, just asking. 
 
😂 Sure that is all possible just for fun of it. If you are a machinist with many thousands of dollars of equipment just sitting there waiting for the project. Or, the ability to make what you need and the time to waste. Otherwise it's likely as stated above, not worth the money nor time to do so. 

I have seen some beautiful guns made and extensively modified though just cuz people could though. So, it's not like it hasn't or will never be done. Because, I am guilty of doing this kind of thing myself.

https://www.airgunnation.com/topic/the-true-cost-of-my-60-crosman-2240/?referrer=1
 
Points well taken BioHazard. I may not do much of anything, but such decisions can't be made until one knows the impediments and design trade-offs the original designer faced. Sometimes I wonder if performance trade-offs might be made because of marketing decisions, like how many shots a 12g cartridge will deliver. If I'm willing to have fewer shots per, maybe there are ways to tweak toward my own preferences. Etc. If the issue is predominantly barrel length, however, then obviously an integral barrel would be hard to replace just to get another 10% of speed. Basically I'm wrestling with the trade-offs first, and any decisions on what to try (and what that is really worth) would follow. (And of course it goes without saying that regulations are part of the picture.) Thanks for the comments and the link.
 
Tnx Odoyle, I'll check that out. I mentioned above that regulations are part of the picture, but safety is bigger yet--only fools go to the line and beyond, especially just for hobbies.

Such a tether scheme almost suggests that oomph is the main ingredient needed to bump velocity, rather than mere on-board regulator adjustment. And maybe that's the case--if so at least it's a data point, and really what I'm after is ideas right now. A tether scheme would also inherently degrade one of the primary features of revolvers--their portability. Still it's very interesting; thanks.