[mhroczny1337]

Don't know if it helps, but all files are in archives inside of:
/King's Bounty Crossworlds/data/
/King's Bounty Crossworlds/sessions/orcs
/King's Bounty Crossworlds/sessions/red_sands

It depends which unit you have edited.

You have to replace old files with yours; your edited unit.dds should go to textures.kfs, unit portrait (.png) to interface_textures.kfs. Ability icons (4files: normal, onmouse, onpress, disabled) also (.png) to interface_textures.kfs