Most will choose not to, but you can use slower powders in the 44-40, often to good effect.
You will need a chrony. Take a published load such as 11.0 grs of Unique, and establish the MV it produces in your gun (a "baseline"), with the bullet you have chosen.
Work up loads with other slower powders, and stop when the MV produced just exceeds that produced by the "baseline" load. When more or a slower powder is used to develop the same MV as less of a faster powder, the resulting pressure will be lower, so you can safely exceed the baseline MV and still be at safe pressure. The M1892 is chambered by some manufacturers with the 454 Casull in the 60K psi range, so you can play above the standard 13K psi loads for the 44-40.
I've done this with SR4759 (15.0 grs), H4227 (20.0 grs), and IMR4198 (23.0 grs - full case), using 11.0 grs of Unique as the "baseline".