Create and add a Gatekeeper label to the app. (‘Approved’ is an arbitrary string.)
spctl --add --label "Approved" /path/to/xyz.app
Approve all apps with the label.
spctl --enable --label "Approved"
This only needs to be done once and adding the same named label to apps in the future automatically enables their access.
Open the app as usual.
open xyz.app
For more information about spctl (SecAssessment system policy security), see the man page.
This is no longer supported as of MacOS 15+