Restoring inheritance just takes a little prestige. One thing I like to do is keep a backup, disinherited heir in case things go wrong with my primary heir. You can use the disinherit option if you have extra prestige & renown.
There are other considerations as well: I avoid giving my non-primary children an intrigue education. So it's a big, though not overwhelming, penalty. In contrast, a child in the right education with decent guardian (16 in primary stat, 8 learning) will have a better than even chance of getting the tier 3 or 4 education. Even including this though, you'd need a genius child being educated by a genius guardian with amazing stats to expect a tier 3 trait. The success weight gets boosted by the guardian's skills and if they have any of the intelligence traits (the candle ones). The wrong childhood trait adds 20 to the failure weight (taking each roll to a 50-50 proposition), meaning on average, you're looking at 4-5 successful rolls and a level 2 education. The game makes each role with a success weight (60 base) and a failure weight (40 base). (If you have the studious youth perk it's a bit better). On the math side: the game makes 9 rolls for education: 8-9 successes give the tier 4 trait, 6-7 give tier 3, and so on.
