GoS brought plot information that needs consideration if I'm to keep the intention of respecting what Umbra understands as "canon" as intact as possible. Most of it is dealt with relative ease since they fit a kind of plan-B I had stitched for this situation. But some core bits are not so easy - An example:
For any one caring about this project, Charlotte and Jonathan are said to play a role. However, the presence of Charlotte and Jonathan during the war does not quite jive with Alucard's lack of knowledge of them, depicted in GoS. So, the immediate conclusion is that he simply never met them (less likely), or they were dead (more likely). Does this mean no Jonathan or Charlotte anymore, though? You'll have to wait and see.
On the other hand, GoS said a few things I suspected and wrote into Umbra's story in one way or the other, either requiring no adjustment at all, or a very minor adjustment. You lose some, you win some. I can't reveal these, not that it would make a huge difference since people aren't exactly here for "story" in Castlevania, but I'm glad it happened nonetheless.
So, currently I have only a vague idea about how these things can work out and am really not too concerned with it. I'll just rewrite to connect with GoS wherever needed to the
best of my ability, some changes on the few things you already know will take place, and that will be it

To close: GoS is the last CV media that Umbra is conforming to as "canon". By the time a new "canon thing" comes out (if any), Umbra won't bother to reconform from effort reasons to creativity reasons. This is fanfiction, there is no gun pointed at our heads forcing us to conform and, as said on the first page, its only goal is "telling an entertaining story" and now maybe "playing and looking good".