Not sure I appreciate the difference you are making between "alter the setting of a Foot Controller" and "alter the parameter in the Voice that is the target of the Foot Control"

You certainly cannot manipulate the physical pedal with the computer... to manipulate the pedal requires a foot 🙂
Of course, you can manipulate the assigned parameter within the VOICE.

The result would be the same. The Foot Controller value is always a number from 0-127. The value is based on its physical position. How that is interpreted by the synthesizer tone engine is a function of the CONTROL SET assignment ("Destination" and "Depth") and the range available of the assigned parameter.

If set to control Volume, for example, you could set it up so that heel-down is zero and toe-down is 127 (normal use).
You could set it so that heel-down is some specific value, for example, 35 and toe-down is 127.
You could set it so that toe-down is a specific value, for example, 96 and heel down is 0
You could set it so that toe-down is 0 and heel-down is 127.
You could set it so that toe-down is +63 and heel-down is -64, etc., etc., etc.
It depends on the range of values available for the selected parameter. Some parameters have a range minimum-to-maximum (0-127), some parameters travel above and below a center point (-64 thru 0 to +63), or left-to-right (like pan), and so on.

How the Foot Controller makes something behave will depend on what you've assigned and the direction of control.

Sorry. I wasn't anywhere near clear enough. My question is about the situation I described in this thread. In that thread, you told me that a Foot Control would always be reset to 127 on a program change. What I do when I go to that Pattern is to briefly rock the Foot Control with my foot so that I can start off with it set to 0.

What I'm wondering is, is there a way for the VST XF Editor to alter the value of that Foot Control? Or, alternatively, is there some MIDI event I can insert into an appropriate Track (using either Cubase or the XF itself) to alter the Foot Control's value?

What I'm wondering is, is there a way for the VST XF Editor to alter the value of that Foot Control?

The Foot Controller, as a universal MIDI control device, defaults to "maximum" when a program is recalled, as I explained in the referenced thread. Again, you need to choose a controller that defaults to minimum, because you want the Voice to start sans the growl. If you select a controller that defaults to maximum, the assigned parameter will follow and start at maximum.

Or, alternatively, is there some MIDI event I can insert into an appropriate Track (using either Cubase or the XF itself) to alter the Foot Control's value?

Your thinking is in the right direction here. The Foot Controller as a device defaults to maximum... The toe-down position is, by convention, the maximum value. You can understand that when framing the 'reset defaults' for physical controllers, the designers of MIDI decided to always have the controller allow for normal sound when a program is initially recalled. A foot pedal that does volume, for example, would then naturally default so that sound could occur. This is what you want 99.999%of the time. It is the exception, the unusual situation, where volume would desirable to start in the off position. (That would cause more panicked phone calls than a little bit! 🙂

Consider the following:
The Foot Control is a minimum-to-maximum controller that defaults to maximum (perfect for volume)
The Modulation Wheel is a minimum-to-maximum controller that defaults to minimum (perfect for your 'bringing in' an articulation, like your growl).

However, if you don't wish to use the obvious best physical control for "bringing in" an articulation, you could indeed have the sequencer send a message... The fact that this happens after the program is recalled will send a new value to your parameter. It does not change the Foot Controller, it changes the parameter your Foot Controller is being directed to control. But this means you would need to recall the Program, then start the sequencer. This to me is no different from recalling the Program and then rocking the pedal to heel-down position.

Is there a reason you don't wish to use the MW?
How about the Ribbon Controller? It resets to 0 when a Program is recalled.
The PB Wheel can be used. Obviously, it was designed for bending pitch, but if you elect not to use it for this you can reprogram your Voice so that the PB Wheel applies the growl. Simply set the Voice's PB Range to +0/-0, and assign the PB Wheel in the Voice's Control Set to bring in the growl.

The AS1/AS2 Knobs also default to minimum, and can be used.
The [AF1]/[AF2] buttons also default to minimum status (however they send 0 or 127, no values in between)
As does the Assignable Foot Switch.

I suggest, as I did in the previous thread on this topic, you choose a controller that defaults to minimum upon reset/recall.

Hope that helps.

Excellent additional information, that will be very useful to me as I continue to learn how to use this machine.

Your thinking is in the right direction here.

I consider that high praise, coming from Bad_Mister!