I’m on the OKFN advisory board on the Open Definition which also oversees licences, their openness and compatibility. I am really impressed by the other members (I normally have little to contribute!)
What happens when you want to edit a licenced document and republish it? It depends on the licence. Leigh Dodds on the OD Board has compiled (updated) a very useful resource on licence compatibility.
[1]. http://theodi.org/blog/exploring-compatibility-between-data-licences
[2]. https://github.com/theodi/open-data-licensing/blob/master/guides/licence-compatibility.md
[3]. https://docs.google.com/spreadsheet/ccc?key=0AiswT8ko8hb4dEJ6VVhYamlNMWo5WHpSV3IzVzAtZkE&usp=sharing
The problem is that some licences allow editing and modification, and also relicensing, and others don’t. You can convert a CC0 document into a CC-BY-NC one, but you can’t reverse the process. With N licences there are NxN options so it’s useful to use a matrix: http://clipol.org/clipol_dodds_compare.png
Here’s a snippet. CC is Creative Commons and ODC is Open Data Commons http://opendatacommons.org/ from OKFN. CC is the predominant licence in academia; ODC is widely used in government.
Notice immediately that CC-NC-ND cannot be edited or transformed and cannot be converted to any other licence. By contrast CC-BY can be edited and relicensed under any CC licence except CC0.
Licensing is non-trivial. If you try to write one or modify one, however well intentioned, you will almost certainly get it wrong (we debate a number of cases where this has happened and try to decide whether it’s compatible with the Open Definition. So please re-use a licence wherever possible rather than hack your own.