Ah yes, getting corrected by Aazealh, the true initiation process of this forum lol.
Yes and no. The boy could only be born thanks to the Skull Knight's intervention, however the beherit apostle did not swallow it because he had been wounded. He did so because he found in his sad fate (a misshapen baby dying alone) a kinship that moved his heart.
I may have misinterpreted the scene as him taking pity on the baby because they are both dying. The dialogue is "This is... a body of flesh, but it's no ordinary human.
It's dying, it's power spent. You're the same as me, then, misshapen babe. Let us die together."
Bolded part is what I latched onto here. I had interpreted that he was specifically dying because Skull Knight wounded him, since Skull Knigh says "With such wounds, he can't get far" but he might just be refering to his fate in the incarnation ceremony.
He doesn't say that he wants to influence these events in minor ways, not at all. What he means is that during these "junctions of times", not everything can be accounted for and that it's possible to derail the plan. Meaning to impact it in a way that matters. That's why he goes for broke each time: try to take down Void during the Eclipse, try to kill the beherit apostle before the Incarnation, try to slay Femto before he merges the worlds.
The specific line I was referencing, at least as translated by Dark Horse (YMMV), is "Though minute, singular details certainly
can occur at a temporal nexus that even
they can't predict... ...I, in turn, gamble everything on said occurrences."
The way I always took this line was that, though the big picture of events such as the eclipse or the incarnation ceremony couldn't be changed, small details can be fudged because the God Hand can't predict literally everything. This takes the form of things like Guts and Casca surviving (and Rickert too I suppose), and, regardless of if the Egg Apostle had done what he did for the reasons I thought or not, Skull Knight's intervention in the Eclipse still resulted in Griffith gaining a weakness.
Obviously he wants to make big changes, and he does take pot shots at Void and Griffith in these temporal junctions, but I think he knows he can't change things that significantly, especially given his noticing that he couldn't kill the Egg Apostle perhaps because it wasn't "yet time to kill him..." Maybe I'm wrong, but I think he's hinging on all those minute, singular details he's affected snowballing into greater changes as time goes on. Even discounting the boy, it's already true that this is the result of his actions, given all of the things that Guts has done since not dying.
It's a given that the boy was going to be the key to Femto's defeat, but that's not something you can conclude based on the Skull Knight's actions. I mean, he told Guts to kill him right when he was born, remember?
That's why I mentioned that I don't think this is some grand plan he has. He didn't intend on saving Guts and Casca as the primary motive for interfering with the Eclipse, nor did he value the life of the demon child afterwards. It just so happens that these circumstances have arisen from his actions. I think he was just fuckin shit up and seeing what happened, but maybe that's an unpopular opinion.