In this tutorial, I will show you how to make a larva morph into a marine.
First thing you do, go to data editor, choose buttons, and duplicate a morph into zergling. Change the icon and text into what you want.
Then, go to abilities, and find Larva- Morph Unit, and change info
Select a blank one, and change the following to what you need them to be. You can even set the required building here. I set it to spawning pool.
Finally, go to Larva, and Command card
Select any empty slot, and find the button you made at the beginning.
Finally, to finish it off, fill in the following, including the morph you just made.
this helped me a bunch, I was trying to do just that (well not marine) thanx