Assuming the hammer/trigger combination is "matched", that is, fitted at the factory for the period of production of your revolver, it can be a simple drop-in replacement for anyone capable of properly detail stripping the revolver.
If you factor in decades of difference between the gun and the replacement hammer/trigger, long action vs short action, it can get dicey, require fitting, or not work at all.
What is the model gun, year of production, and source of your TT/TH?