It depends on the value you change and what to.
Dark Omen is a bitch for crashing so you need to be careful. General guide
Keep the unit stats below 8.
Keep the number of units in a squad to 24 or less.
Keep the number of squads to less than 16 per side.
Make a save each time you change something to confirm where the error is occuring.
Ask here what you want to do, we should be able to tell you if its possible or how to achieve a similar effect.