The term "Eastercon Charter" has been used for the discussion about whether there should be written rules for running an Eastercon.
There is no Eastercon Charter.
There is an Eastercon trademark which is the only tool we have to restrict who calls their event an Eastercon.
And there's an expectation that an Eastercon will hold the bid session for the Eastercon two years later (and potentially the vote for the convention one year later if necessary because there were no bids the previous year).
After that an Eastercon is pretty much free to decide what they want to do, though of course there is an expectation that they will run a convention that celebrates the rich diversity of SF fandom (books, TV, films, comics etc.) and will probably include most of the "usual" features such as an Art Show, Dealers Room, Guests, a bar, Masquerade, panels, talks, science items, silly items and will be held over the Easter weekend somewhere in the UK.
But as there are no rules, if an Eastercon bid wanted to propose running the convention in Dublin, in May, and with no bar ... then they are free to do so (but would *not* win the bid!) ... and if an Eastercon committee decided to change things too much, then there would be a lot of unhappy people and possibly people would set up an alternative convention and the trademark holder might withdraw the right to use the name Eastercon.
Nevertheless, every few years people gather to decide whether to create an Eastercon Charter ... and every time it's voted down.
Note that there is currently a website and discussion on the future of Eastercons at http://eastercon.wordpress.com.