Without looking at the script and assets in their entirety it's hard to say what's preventing regicide from working. You could try making a copy of the transform and adjusting the settings, though the defaults should be enough.
The frame rate issue, as you suggested is an engine quirk. That's Ren'Py's default behavior you're running into. If you add this to any transform you're actively using, Ren'Py will render at full FPS as long as that transform is in use. It's worth noting that the shaders were written with this in mind and most of the included shaders do not have any frame limiting in them. This isn't a problem for most of them, but any of the shaders that include noise effects might be excessively animated as a result, depending on the resultant frame rate.
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