I think that for the most part, the settings on the units are not changed during live shows. They are, do, however, seem to be activated by the members of the band (at least in Ed’s case). Ed also, for the most part, switches presets on his Korg A2 by himself, and has used many different means to do so over the years.
As you can sort of see in this extremely blurry image, Ed initially used a Korg FC6 to control his Korg A2. The FC6 is the dedicated controller for the unit. It was used until circa 1997.
I suspect that for songs such as Punchdrunk Lovesick Singalong, on which one of Boss Delay rack units was likely used, the delay used on the song was kept at a single setting, and manually activated by a tech prior to the start of the song.
By the OK Computer tour, Ed had switched to using some sort of dual footswitch controller, which is the black and white unit in the photo above. This was likely used to cycle presets on the Korg A2.
I am unsure of what was used for the following years, and I suspect that a tech likely took a more prominent role in controlling the rack units.
In 2006 and 2007, Ed used a Roland FC200 to control his rackunits. This was used in conjunction with a Sound Sculpture Switchblade. The switchblade continues to be used to the present.
By 2009, he had switched to using a Voodoo Lab Commander for the purpose. You can see that the footswitches are labeled things such as “A2 5,” A2 2,” and “TC ST,” which likely respectively refer to presets on his Korg A2 and probably on a TC Electronics rack unit.
Finally, in 2012, Ed began using the Tech 21 MIDI Mouse himself to switch presets on the Korg A2, and sent his signal through the rack unit (which is therefore always active) with a footswitch on one of his bypass units.
However, it should be noted that at some point in the late 2000’s, the Korg A2 was controlled by a Tech 21 MIDI by a tech who also controlled the mixer for Ed’s setup. This seems to have been used alongside some of the other switcher units, but perhaps was preferred for live performance, whereas Ed might switch on his own during recording sessions.