I realize that the functions of control with a handheld are lost with the addition of the board into the DCS-RC, but with a longer timed reset cycle could you send a data string to a engine between resets?
Yes you could. Obviously the factory-stock DCS-RC without the PBW (perpetual barking watchdog) board has a much longer reset cycle time of forever (it never resets unless you remove power)...and during that longer cycle is when data strings are sent to the engine under handheld control.
When you get your boards back, if you want to experiment with a longer reset cycle, probably the easiest is to put a capacitor in parallel with the existing capacitor. That is, it's arguably easier to tack a capacitor in parallel with an existing one (to increase it's value and hence the time delay) than to add a resistor in series with an existing one. It's the product of the R and C that sets the time delay so a 10% increase in the capacitance would increase the delay by 10%.
But, to repeat, I think you need to confirm your unmodified DCS-RC can start your PS engine silently in command mode in the first place. Again, I realize the TIU sends its watchdog for up to 45 seconds (depending on TIU Rev) but the fact is the DCS-RC sends that single 1/10th second burst just after it receives power. And that seems to be all that's needed to force a PS2/3 engine in silent command mode on power-up.
Another thought. I realize you'd need to factory-reset your engine to the default DCS address but did you confirm that your particular unmodified DCS-RC can in fact control an engine using the handheld remote?