Hello,
What you are asking for IS in fact possible, but it would take a considerable amount of roleplay, skill building, resource collecting, and building on your part. I would suggest that you look at the
monster wiki and look at things called "Moldlings". There are a couple playable moldling races, such as the
Kelvic and the
Pycon, created by powerful wizards, researchers, and innovators. Creating entire races and beings able to reproduce after magical tampering takes a lot of time and research. An example would by my own (incomplete) race
The Vinonen. In the first post you can see the entire process laid out with alchemical chargers and procedures.
It would be far easier to create 'monsters' that will serve you until they die (things that are unable to reproduce). My primary focus has been on Alchemy, but I suppose you can use a good bit of Philtering to change a creature.
I would suggest that you read lore pages very carefully and come up with a plan of your own to create what you'd like. Im sure you can figure something out. Though the path of the moldling is very difficult and takes lots of careful thought and preparation. However, it is something you could work towards.
Though if creating something isnt what you want, I think we discussed actually 'becoming' something. If you can get to master morphing, you can unlock supreme transformations which can be fun to play around with. Expert in morphing should be enough to turn into a giant bird if you have a model of it.