It's infrequent enough that I have to do this that I forget how. So to help me remember, I'm posting it here:
To make your permissions changes to devices in /dev/ survive reboots and become permanent, you need to alter the device permissions in
So for example, say I have a created a group that holds all users on the system that are to have RW access to the video capture hardware (such as mythtv and zoneminder), open the perms file and look for this line:
0600 0600 root
This v4l class covers all /dev/video* devices. To make them RW by the group "video", change the line to look like this:
0660 0660 root.video
You can reboot to see the effect.