I don't think you can "set" vendor prices and supplies multipliers for Honor mode, though?
That's just for custom mode. Honor mode has its own set values as far as I know.
You have to intentionally die once in Honour Mode in order to access the Custom options with the Honour ruleset. Hopefully they change this with the next patch.
Except for the rule about Giant Hill elixirs (which I still used sparsely even if i didn't have a hard rule against them, since i was a cheap-ass and I didn't realize it was my CHA 8 barbarian that made everything look so expensive).
Not to mention that it's NOT EVEN CLOSE to be the most powerful elixir around, anyway. There are a bunch of these that run circles around it.
My problem with it is not that it's the most powerful elixir, it's that it's so readily available at the start of the game and immediately enables builds like Tavern Brawler monk or an archer build using the Strength bow you can buy from the Zentarim guy. The better ones like Cloud Giant elixir are much harder to come by early game.
On one hand from a dev perspective I can see why you'd want to give players options like that, especially on Honour Mode. But I'd rather eliminate it as an option for myself to make it harder.