OK, I managed to clean up my preset scripts with a custom inspector!
STMPresetController https://pastebin.com/pZymy31R
STMPreset https://pastebin.com/9mXe2emT
Add STMPresetController to whatever gameObject has STM on it and you want to control with a preset. There's a "NEW" button that will create a new preset based on the settings of the STM object.
Once a preset is assigned, "Copy Super Text Mesh to Preset" will re-apply settings to the preset as if it was newly created, "Paste Preset to Super Text Mesh" will take the settings on the preset and send that to the attached STM object, and "Paste Preset to ALL" will do the same but to every STM object in the scene. I was going to make this automatic, but it's just an editor tool so it would be impossible to run on presets not open until they're open... So I *could* have it run during runtime OnEnable(), but for now it's just there to apply multiple settings at once.
So... if you had two Preset Controllers in a scene, changed the settings on one and pressed "Paste Preset to ALL", the changed settings will apply to all STM objects with the same STMPreset assigned to them.
The settings are limited to Font, Size, Quality, Filter Mode, Line Spacing, Material, and an option for Base Offset at the moment since those are what I think is most relevant to this, but it could be expanded later.