Two ways come to mind:
1. It has been said that you can change the starting roster characters – so in theory you could replace either the starting vestal or PD that first arrive in the coach. (I do not know how to do this).
2. Alternatively I have added more heroes to the tutorial – see my “Lord of Darkest Dungeon” mod on the nexus. In that mod I have added custom heroes to the 3rd and 4th party slot. They then stay with your roster after the tutorial just like Dismas and Reynauld. So you could do something similar with your own custom heroes.
Current class mods/variants:
Shadow-Dancer, Maiden, Knight, Dame, Evoker, Warlock, Apothecary, Psionic, Treasure Hunter, Gladiator, Blackguard, Valkyrie, Shadow Valkyrie, Vampiress, Lycan, Court Magus, Songstress.
DOWNLOAD FROM: http://www.nexusmods.com/darkestdungeon/?
My personal Art work and Novels: www.stevenmouland.com