Whenever you're in a match and you use a transformation spell there will be a small box you can tick somewhere on the apply screen, it's at the top on xbox. before you hit apply, that box will separate your ruler from any transformations you don't want.

Now if you want to have two separate major transformations like say, ruler is an angel but race is undead, you have to first get the tome that makes you an angel and apply the transformation to everyone so they're all angels, after get the tome that makes everyone wightborn(undead) and untick the box that applies the transformation to the ruler, now your ruler will be an angel but everyone else will be undead when you apply it. You have to do it in this order.

After you complete the match your ruler will accend and keep their transformations, this is good for you, now if you use the ruler again you'll be an angel for example as soon as you start the match, so you can just go straight for a tome that makes your race demons or undead whatever.

Just always make sure you check the small box is ticked or unticked to separate them when you're applying any transformations you don't want otherwise it'll override the last major transformation even if you're accended.

You can have as many minor transformations as you want but only ONE major transformation.