I started a new game with this mod and a long-reach mod installed, and this mod seems to have overridden the long reach mod, resetting everything to vanilla reach. I can't edit the settings since the game has already started, so my only option is to disable Picker Extended, which is a shame, because I do like the other features.
Would it be possible to add a toggle to the mod's reach component? (For that matter, would it be possible to add toggles for all of the mod's features, in case part of the mod interferes with other mods a player has?)

You can edit the reach settings in the mod startup options.

The startup options can't be changed after you start a game, unless I'm missing something. I've also tried editing startup.lua, but that doesn't seem to affect the game at all after map generation.

Don't edit the .lua files. Before you load the world you can go into mod options and on the startup tab change any values you want.

Ah, my mistake. Didn't realize you could edit the mod settings from the main menu.