Only1catar,
Most things can be done in DB Programming if you know where to look.
For the flag the easiest place to go when doing large groups is System > Phone Related Information > Flags and find the flag you want to work with, in this case Do-Not-Disturb Override. When you click on this you can pick the phones you want to have it and leave the rest off the list and then accept it.
As for the button there are a couple of different ways to do this, which sort of depends on your phone types and keymaps. In the end you need to find or create an open key position on the phones you want to have the ability to override DND on other peoples phones. Once you have found the key it depends on whether you want it to be hard-coded or not. If you want it to be hard-coded then you need to go to System > Phone Related Information > Keymaps and find or create a keymap that will work for the phones you want to have this key and then set the key in the keymap as a Feature Code. If you don't care if it is hardcoded or you don't expect the user to change the key at some point in the future then you can use a User Programmable Key to do the same thing. This is easier to implement on keymaps that are tied to multiple phones, but you don't want them all to be the same. If you choose this option then just remember which key and its User Programmable Number and then go to the phone itself; System > Devices and Feature Codes > Phones > Programmable Keys > Programmable Key Number and change it to a Feature Code key and then program it with the code you want [373 by default] DND Override.
Thanks,
TE