ORIGINAL: Sabranan
Looking at it it does seem odd that you could research Advanced Colonization without having researched Colonization at the very least!
Leaving that aside though, I would think to do what you want you'd have to remove Enhanced Scanners as a parent of Stealth, then make an intermediary tech with Far Sight Discovery and Enhanced Scanners as non-obligatory parents. Then just make said intermediary tech an obligatory parent of Stealth. That does mean either having a project that has a parent on the same tech level (which looks a bit weird), or increasing the tech level for each tech after Stealth to make room. That would of course change research costs for Stealth and the 7 following techs you'd have to shift over, but you could correct for that with the Base Cost Multiplier.
Yeah, I thought about introducing an additional node where all of the parents are optional, and then make that a mandatory parent of Stealth. But it would have to cost 0 to not impact the other races. And not make any of the other techs change in cost. Even then, it would be, umm, less than elegant?
Maybe I'll play with cost modifiers tomorrow and see if I get any bright ideas.
