Thanks for your comments. In an attempt to make sure that we make the best use of the accounts that we have, we have always taken a liberal approach to who has access and can use them (especially the Twitter). Access details are in the ambassador pack and, in order that the Twitter reflects the wide range of activities that OKAu undertakes around the country, my view is that all local organisers should be free to use the account.
Personally, I'm against single-use Twitter accounts for events as I think that they're less effective. Others are, of course, welcome to differ - most GovHack sites have dedicated accounts, for instance.
As for an "over-arching communication strategy", I think our goal should be to share as much of what we do as openly as we can with our community. That includes making the most of the channels which are already well-established. Personally, I be loath to see these sorts of procedural matters making their way into the Code of Conduct and I'm also hesitant to create too many rules, as I feel they can have a chilling effect. If you feel that some guidelines would be useful, feel free to put up a draft to the community.