[quote=@Dead Cruiser]
As long as we're floating ideas, I wonder if I couldn't spin a matched pair of a scion and a rogue to you. I know you pointed out that you didn't want one that was the servant of another or something, but I have them imagined as something of a conjoined pair that hate each other. To be specific, I was imagining a scion in the form of a sentient, malevolent sword being wielded by a more grey character. The latter would be more my "character" and I would only be writing his CS, as the sword obviously has far less agency. Perhaps she's trapped in that form as a "punishment" from Chernobog... anyway, I have ideas.
[/quote]

That's definitely something that could be done without needing to bend the rule. It could be a different take on the "alternative path to power" for scions mentioned in the OP:

[quote=OP]
It would perhaps be possible for a mere mortal, through ambition or curiosity or some other compulsion, to ascend to the status of a scion. The most likely way for this to happen would be for the person to come across one of the Chernobog’s body parts and take in its power -- willingly or otherwise.
[/quote]

I see no reason the fragment of Chernobog in this scenario couldn't be replaced with something like a scion imprisoned in an artefact, so feel free to develop the idea further. I'll be looking forward to seeing what everyone comes up with.