Cannot register Heavensward:

[Legion88]

Both are suosed to be windows. you need a new account by SE to register the new one. steam and the "normal" version can't coexist on the same account.

But if steam records the playtime from the greenman version it is a steam version or an other extra version who can't coexist with the other.

[Acteon]

To clarify; by "new account" do you mean a new SE account? Or a new game account?
My main point of concern is not losing my character.

[Acteon]

Well it would appear the issue is solved.

To anyone who might suffer this confusion in the future:

Greenman Gaming sells Windows copies of the game.
For whatever reason; attempting to purchase a windows copy of Heavensward off the Enix store was incompatible.
I've gotten word back from my help ticket that the issue was resolved.

Attempted to re-add the Heavensward key to my account; and it now works!

My thanks for attempting to help, Legion88; but I covered the steam / nonsteam issue in the original post.
This appears to have been an internal problem of some kind that I'm lucky enough for SE to have resolved.