I'm describing here the controller's function for HD EDIT. At the pod it is also available when you double click the MOVE button.

What we have now:

If you set a range from 20% to 50%, in the moment it is meant to do it as a continuous controller like the EXP pedal, so you can increase or decrease the drive parameter.

To toggle the effect on/off you can assign a footswitch like FS1.

Back to your question:

Because FS1-FS8 are switches, I understand that you would like to switch between drive at 20% and 50%.

Especially if you already had a wah routed to EXP, you would then have another independet controller to change the drive.

The FS that toggles the fx on/off cannot change the drive at the same time, so e.g. you might want FS1 for fx on/off, and FS2 for drive switching from 20% to 50% and back.

This is a disadvantage, because sometimes you need to press 2 different footswitches for coming back to default/ saved preset values, like fx = on and drive = 20%.

It wouldn't come into being if this fx would be on permanently.

Result:

On the one hand side, it would be interesting to have parameter switching, on the other hand side you can already realize it by simply changing the preset, although there is a short audio break when switching.

This is my point of view.

That would be a nice feature to have, but for now, you can do what you want to do like this:

Put two screamers right next to each other in your signal chain. Set one to 20% and the other to 50%. Keep all other parameters the same.

Now turn one of them off, and assign both screamers to the same FS. That means that when you click that FS, you will switch from one screamer to the other. Click it again, you switch back again.

Yes, it wastes DSP and an effect slot, but it does what you need it to do.