I currently have a S9V31 whip and a SG-230 remote tuner (200 watts max)
I do not want to change out the antenna because it provides me with the pattern I want

I am considering going to the SG-235 since it can handle 500 watts.
The issues is the SG-235 only has a max inductance of 32 mh (the SG-230 has max of 64)
The SGC 236 only had a max capacitance of 400pf (the 230 has 800) put I do not believe that will be an issue.

My thought install a 32mh coil in a separate box with a NC relay to short out the coil on all but 160 meters.
On 160 Meters I will energize the relay opening it and the coil will now be inline providing the needed inductance.

I want to maintain the tuner remotely (at the base of the antenna) since it provides the best power transfer (most efficient).

Thoughts?

Put the loading coil at thefar end of your wire.
it will, in effect make the wire appear longer at 160M, and be  essentially invisible to the higher frequencies.

Remember,  with the auto antenna coupler, resonance of the radiator is not necessary.
Th e antenna coupler is basically an active impedance matching device.