My car allows regen when the battery falls to 98%, within the first mile of driving. I get that folks who regularly go down a hill after charging might like to regen right away.
Regarding charge limits - the developer of an open Kia/Hyundai API and I recently experimented with charge limit queries, and were unsuccessful. All we found is Kia (via the API) does appear to talk to the car when a properly-formatted charge limit command is given. Yesterday I opened a ticket with Kia CS to try and find out what should and shouldn't work.
The Kia Access app also allows one to try and set a charge limit for the PHEV... that fails with the same error I saw when directly querying the API. It's either a mistake; modifying the charge limit is not really an option, or it should work and the current Access implementation just has a bug. The vehicle info query response includes an AC charge limit of 100%, exactly like the EV reports AC and DC. For the PHEV I'm starting to suspect it's really a read-only object, given it's not settable on the dashboard either. (In the EV, both AC and DC limits are settable.)
Even if it starts working it's not something I'm likely to use, and am pursuing it mostly as an exercise to explore and learn the API. The potential for automation is impressive - though you have to watch out for excessive 12V battery drain from frequent car queries.