Pico-8 should have an option to quickly switch to x2<->x1 display resolution, and a way for programmers to automatically set this option when starting a game...
Someone asked Pico-8's author about this feature request?
(Amazing work BTW! Thank you!)
Controlling resolution from lua would be more convenient for sure. I get the impression the hi-res mode was intended to be just a novel undocumented easter egg rather than a seriously supported feature; in one version Zep actually removed it completely from html exports! I was very grateful when he was receptive to adding it back in the next version. :)
Maybe if more people make multi-display carts it might become higher priority? (Writing carts to use it does add another level of complexity though, and can require 2x or 4x CPU compared to a single display cart, so it's not always feasible).