is there a way to write into a patch a selection for input and output devices? like a [loadbang] that would, upon opening the patch, assign the desired device?

yup some menuitems can be intercepted with [r pd]

see attached store-audio-settings.pd

open the patch, make your audiosettings, save and close the patch, change audiosettings, reload patch to restore audiosettings

mvh

http://www.pdpatchrepo.info/hurleur/store-audio-settings.pd