Welp, after living with it for a few days, I think I can call this workaround a success. I haven't seen a check engine light at all since installation, and it passed inspection with no issues. Anyone looking to modify the thermostat in their '01–'03 2.3L Ranger, this seems to work. Just buy a newer thermostat assembly (the Motorcraft unit without a heater circuit. I got it by looking at parts for an '06 2.3L), and then tack a resistor between the wires in the connector. Just keep in mind that one of those wires is 12V, so be prepared for that resistor to get a little warm. I mounted it to that metal bracket for a reason.

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2003 Ford Ranger XLT
2.3L I4 Duratec DOHC, 5R44E 5-speed auto, RWD, 7.5" Open w/ 4.10 Ratio, Gibson split-rear catback
Sonic Blue Pearl with dark gray trim