Questions about overhealing

[Arcaloid]

Do the overhealed amount generate aggro in the same way as actual health healed?
they generate double aggro than effective heal

Do Regen or Eos HoT overheals generate aggro as well?
Yes

Is HoT aggro generated each tick or at the start/end of the spell duration?
each tick

Can you check how much as overhealed in parsers or in-game combat logs?
don't know, never used a parser

Are SCH adloqium shields affected in any way by overhealing? (overheal boosting shield or overheal reducing shield strength)
I believe no

How bad is it to overheal in general in XIV? How bad is it to overheal in HM Primals compared to Coil? Help a fellow healer out here!
In general, it's bad, but a couple times in a dungeon run is acceptable.
In primal fights it's not too bad because there are no adds, and tank usually take constant damage so healer can't really overheal much.
In coil, turn 1 and 2 are same as primal (single BOSS), but need to pay more attention in Turn 4 & 5. However, still it's not that bad because tank usually take so much damage that WHM can use Cure II all along and just be able to keep tank alive.

[Pikken]

Do the overhealed amount generate aggro in the same way as actual health healed?
they generate double aggro than effective heal

I think the double is incorrect. But overheal does generate aggro, the same aggro as normal heals. So in other words one Regen or one Cure will generate the same aggro regardless of how much HP the target has (disregarding crits.)