What one man does to a revolver doesn't make it a Colt factory product - a shame, in some cases - but for the best in others.
As an example - Elmer Keith ruined numerous Model P's by adding various backstraps and triggerguards from M1860's and Dragoons and Bisleys - but that didn't make them a factory product - custom or otherwise.
Keith turned 'em out, shot 'em - destroyed more than a few - and if he liked them - usually had them engraved and plated.
All this eventually led to the Ruger Bisley - a revolver that was the culmination of a Keith project and not anything that Colt began.
As to Bass Outlaw - this from "Firearms of the American West 1866 - 1894" - by Garavaglia and Worman - page 290.
"Colt Single Action .44-40 (frame #42870) modified for fast close range shooting by fanning the hammer. The original backstrap and triggerguard were replaced with those from a Colt M1872 .44 "Open top" and the cylinder is held in place by a special base pin secured with a thumb screw. The trigger has been removed and the trigger slot welded closed, with most of the guard discarded. The barrel has been cut to only three inches. The weapon was given in lieu of cash to the undertaker who buried ex-Texas Ranger Bass outlaw, who was shot to death in El Paso by Constable John Selman in 1894.(Courtesy El Paso Historical Society via Robert E. McNellis, Jr.)"
A gun actually associated with Outlaw's ownership was a Merwin, Hulbert .44 Pocket Army, taken from him when he flourished it "in a manner calculated to disturb the inhabitants of said public place" in an El Paso, Texas, Saloon on October 15, 1892.
That's on page 328 of the same publication.
I didn't read the article in "Guns of the Old West" as I've found little historical accuracy and more B-Movie writing than needed, but if you read the above and if you can view the picture of the revolver - the work is typical of a blacksmith/gunsmith cobbled-up gun, and nowhere is it attributed to actually "belonging" to Bass Outlaw - but rather to John Selman - who used it in place of cash for a burial - indicating that Selman didn't place that much value on it.
Was it his?
Hard to say - given the fact that Bass Outlaw was pretty well-known and his personal guns would fetch more money if sold by Selman - as were many famous guns by lawmen to supplement meager pay..
Even more were sold by telling someone they belonged to famous folks - Frank James' selling Jesse's guns comes to mind - he kept them out in a barrel - out by an outbuilding - and sold them to the curious.
Scouts Out!