Would there be any advantage for the reloader of Ruger Blackhawk 45 Colt revolvers to use 454 Casull brass, trimmed to 45 Colt length? The brass is intended to be used at significantly higher pressure, so what effect would using such brass have on, for example, number of reloads each "45 Colt" (trimmed 454) case would yield until no longer usable?

No. Unless you want to spend more $$$ for brass and case prep time.

I have two Ruger Bisleys that are Five shot customs that I routinely load to .454 Casull levels using Federal and Starline brass. I have lost more cases by stepping on them than to pressure related issues.

I have mic'd sectioned .454 and .45 Colt cases and have not come up with a difference that is meaningful. I don't or never will know for sure but I bet that the only difference between .45 Colt and .454 Casull cases from a manufacture such as Starline or Federal is the Bunting operation to swage the primer pocket and head stamp and the final trim length.

I don't know if there is any advantage to making 454 brass into 45Colt length, but I trim 454 down to slightly longer than max length 45 brass and load 23.5 grains of H110 pushing a 335 grain LBT GC bullet at 1290 ft/sec. I didn't do this for higher pressure but I just couldn't find 45Colt brass anywhere and got tired of not being able to load for my latest revolver acquisition, so when I saw 454 brass in stock I was willing to pay a little premium and ordered 300 of them. The velocity of my load is very consistant but haven't shot it off a bench to see how accurate it is yet. BTW, this load is for my (old/large) Ruger Vaquero, so don't use it in the new Vaquero or a SAA as you might put pieces of it in orbit and/or hurt yourself or others nearby.