Entirely New UI/UX

I am graphic designer/UI/UX designer and have sort of a strange question. I am aware that launcher/lock screen replacements exist but I am wondering if it is possible to change the entirety of Androids user interface?

From what I understand the launcher and lockscreen are apps that can be replaced, but taking this idea to its logical extreme could someone essentially create an entirely new UI, similar to HTC's Sense, but one that changes the way that the phone deals with homescreens/multitasking etc? I understand that this would be a very large project but I am looking for a basic understanding of whether or not this is possible, how it would work, and what would be required in terms of programming and resources. I am a pretty new programmer but have access to some resources to at least get this started. Any help or pointing me to another forum/resource would be great.

Thanks.