Railroader:
Please post a link to those servo and a wiring diagram telling what signal You intend to reverse, and links to the motors and coolers in order to size the drivers needed.
I'm not 100% certain on the parts yet, but they should be pretty close to these:
Servos: https://media.digikey.com/pdf/Data%20Sheets/Adafruit%20PDFs/169_Web.pdf
Fans (B044): https://media.digikey.com/pdf/Data%20Sheets/NMB-MAT/bg0903.pdf
TECs: TEC-30-39-71 Wakefield-Vette | Fans, Thermal Management | DigiKey
Looking at how servos are wired, it doesn't look like you can simply flip the connector as the PWM would get hooked up to the negative line in that case, but would something like this work:
They just switch the pins the +/- wires are attached to in the connector. That's what I was hoping I could do to reverse the direction vs. using another shield.