From a UI Dev who's most likely to make character sheets.
Here's how I imagine a "Theme Manager" being most useful for all parties involved:
Allow a total/partial UI overhauls of colors/fonts/etc without the UI Overhaul module having to specifically target individual modules.
This is a pair of scripts which do the same thing for different modules. Neither of the Jack Kerouac animated effect modules register with the Sequencer Database out of the box, but these scripts will do that registration.
To use these, either put them in a macro (the same macro will work fine) which you manually run before trying any sequences with these in them, or in a world script. Modules like Hook Macros or World Scripter will let you use a macro as a sort of world script.