How do you change a unit art with an ability?

[SnipeShot]

I am making a vamps map and i want my peasants to have some sort of avatar where they can turn into a worgen builder that i found in the models. i have tried to edit avatar but couldn't really understand the how to with that. then i tried to trigger swap the unit for a worgen builder unit that has better stats, it worked until i tried to swap them back; but i have a feeling the peasant i swapped it back with wouldn't have a cool down for the next avatar. I also tried to change the art w/ a trigger but couldn't figure that out either. please help it is the key to my map that will set it apart from others.

I could make a separate game mode that red can select or make it where the change will be pernament but i prefer to have it as a 15 second avatar deal where it will change back into a peasant.

 

[SnipeShot]

i figured out how to make the change and would like to thank hives because i learned a lot just by reading some of the posts even though none were an issue i am experiencing at the moment.

instead of using a trigger to make my peasant be replaced with a worgen or special effects to create an image, or even changing the avatar art model file or attachment points.

instead i tried to use the bear form and did the following to the ability.

copy paste the ability to custom and edit the following data and techtrees.

Data-Alternate Form Unit Worgen Builder
Data-Normal Form Unit Peasant
Techtree-Requirements none
Techtree-Requirements-level none

i will add a cooldown and tech to it to fit my vamps map later but this is good for now.

after setting the ability i gave the worgen builder the bear form ability and my peasant the bear form and it worked like a charm.