What rules can't we change?
- The platform that we're operating on is a 'given', since it's shared over so many sites. (We would have to fight long and hard to get special programming changes.)
- Basic StackExchange quality expectations as expressed in standard elements of the FAQ, such as the the sections on Etiquette ("Be nice". "Be honest"), and on closing poor-quality questions and removing questions and answers.
What rules can we change?
- Our scope -- it's wholly within our gift what questions belong here and what don't.
- The degree of subjectivity/non-constructive questions we tolerate.
- Our judgement and the corresponding guidance we provide on what makes a good question and a good answer (as long as we stay within the basic StackExchange expectations).
Edited to add: we don't have the freedom in any way to fill our site with crap.