So I was making a human body, marked all the seams and unwrapped it. I then went ahead and manually optimized the layout. My question is, if I want to add a new part to the body (with new seams) to the existing UV layout without clearing it, how do I do that?
Anyone? Would appreciate the help guys. Thanks. 
With such a limited bit of info, I can only give you a limited answer select the faces you want tu re-unwrap and press U.
If you want a more specific answer give some specific information, at the very least annotated screenshots describing exactly what you haver and what you want and a link to your blend file.
Alright, I’ll try and explain this better. I don’t have screenshots/blend file since it’s more of a general question.
Let’s say I was making certain model. I finished the modeling process, marked all the seams and then unwrapped. I then proceed to manually edit my UV layout to use the space I have better (moving around things, enlarging certain parts, etc.), since this is going to be a game asset.
My question is, if at some point in the future I decide to redo or add a certain part in my model that require new seams, naturally I’d have to unwrap the whole thing again right? But that’ll reset my modified UV layout back to it’s original form, messing up my existing textures along the process. So is there a way to unwrap a newly added part into an existing UV layout without resetting the whole thing?
Hope I made myself clear this time.
If you select geometry in the 3d view and move then move it in the uv editor, it will split those faces apart from the rest, you can also use “Select Split” (Y) after selecting stuff in the uv editor and then it will only move the selected faces without the connected parts. I prefer the second method as you can enable “Keep UV and Mesh selection in sync”-Mode to always show you the whole UV layout and work in both views as required.
If you change your geometry, you may also want to unwrap just parts of your model again, all the unwrap operators work on the selection so it wont affect unselected parts of your mesh.
Thank you, exactly what I needed.