Install Dragon Age Ultimate with existing Origins on PC

It should just work. However I know from experience that won't always be the case.

Be sure to check this page if not all the DLC is present: https://social.bioware.com/user_entitlements.php

If you're still encountering issues, please contact support. They can investigate and merge the game entitlements if needed.

https://help.ea.com/article/welcome-to-the-new-and-improved-ea-help-center#contact

Thanks David for the quick answer.

So - If I understand correctly - I can register the Ultimate copy and - after that - try to install only DLCs and Awakening.

To this regard, if I understand well, Ultimate's DVD 2 contains only Awakening and installation should be independent from DVD 1 containing Origins...