I don't know officially or anything, but I'm sure you could release it (as long as you don't try to make money off it obviously). I would say it would be unlikely to impact sales negatively, a lot of people who play custom mods on Original Sin are likely to have Beyond Divinity already and if not and you enjoyed someone's recreation of it you might be encouraged to try out the original and buy it.
It's a different engine anyway so it will not be the same no matter how polished you make it. Remakes never fully replace the original either, for example I played Ocarina of Time on the 3DS recently and as beautiful as it was I would still play through the original version ahead of it.
Also as the combat here will be turn-based instead of real time it will play differently.
I guess relatively similarly, there were remakes of games using the Neverwinter Nights toolkit before and they were not taken down, there's one of Diablo that takes the sound directly from the original. Though I would assume Blizzard just don't know about it. It's also not great.
I'm sure Larian wouldn't mind somebody put the effort in to remake on of their games in their own engine, it would show how much you loved it! Also they seem to encourage the idea of remaking Divine Divinity with the toolset too.
So good luck, it sounds quite ambitious.
