New creatures for Heroes V.

Is there a way to replace creatures without changing their stats and abilities? I'd be grateful, there are tons of very nice models

The possibility certainly exists — you need to open the mod, go into the GameMechanics folder, then Creature, then Creatures, etc. In the last folder there will be a file with the creature's stats — that's what needs to be edited

Two lines control the appearance in battle and on the map
<MonsterShared href="..."/>
<Visual href="..."/>
Those lines must not be touched, but everything else can be changed. The original abilities and unit stats can be found in the data.pak file along the same path as the stats in the mod