I've gathered that you can create a new steamwork pet through Full Steam Ahead, but does changing an existing pet's color work the same way? I want to change one of my pets to steamwork if possible.

Yep! You still need the Yunium Key and the schematic for the type of steamwork pet you want, and then when you bring both of those items to the place where you create steamwork pets, it should give you the option to either create an entirely new pet or change one of your existing ones.

Thank you!!