Thanks very much! I just added some further details to describe a customised DND toggle feature which uses the “DONOTDISTURB” custom device state.
In this way when DND is set using an assigned line key as a speed dial, the usual audible confirmation is heard per the standard DND-toggle app (*76 feature code) however:.
← the Cisco-style DND animation 
is now displayed rather than
← the ‘BUSY’ animation 
- which I think gives a bit more useful presence information.
{edit 14/03} - I’ve updated the blurb above to include settings for using SIP NOTIFY to reset or restart these phones. I’d completely overlooked this before, but so simple to get working!