Thanks for the input, joecozzi and coirbidh_99. I have figured out the external 3 button momentary vs on/off option in the Performance Parameter edit mode on the H90; and I have gotten it to work as desired after editing a few individual performances. My error was that I was going about it in the External Control page in the System tab of the editing software; as opposed to the individual Performance Parameter mapping section on the pedal. It is definitely a flexible option to be able to assign and tweak the controllers on each individual performance preset, and I would not want that option to go away.
However, what I meant earlier is that it would be nice if there was a global option to have the external 3 buttons map out to the second page performance control switches across every performance. Basically, implementing the highlighted text below, but having it work globally across every performance.