I was looking for the "apply_to_all_surface" function in OSC under /media/selected/ but the option is missing that intended?
No it's not. Thanks for the feedback. We'll fix it in 3.0 beta 2 (out this week).
Another solution for now: create a root "Group" that contains all surfaces and assign a control to select this group "/surfaces/GroupName/select", then changing visual selection from control will assign it to all surfaces (since they're all inside the group)