Are there any official guidelines or rules for editing (others') questions?
and/or
What is your opinion on what is reasonable?
If someone seriously changes my question in a way I don't like, (when) is it appropriate to "roll back" these changes? And is there a simple way to do it?
Are there any official guidelines or rules for editing (others') questions?
There's the Help Center, which is searchable, but specifically:
Any time you feel you can make the post better, and are inclined to do so. Editing is encouraged!
Some common reasons to edit are:
to fix grammatical or spelling mistakes to clarify the meaning of a post without changing it to correct minor mistakes or add addendums / updates as the post ages to add related resources or hyperlinksTry to make the post substantively better when you edit, not just change a single character. Tiny, trivial edits are discouraged.
Though you should check the specific sites, there may be differences.
e.g. Stack Overflow Edit page
General:
If you search the site you'll find all sorts of related discussions.
On topic:
How to handle large suggested edit from possible collaborator?
Approving overly substantial edits to answers
As you've not been terribly specific:
Should users edit other users' posts to correct grammar and spelling problems?
What should I do when a user repeatedly rejects or roll-backs valid edits to his/her post(s)?
Was it correct to roll this edit back?
Other possibly related:
What should I do when a user repeatedly rejects or roll-backs valid edits to his/her post(s)?
Is it OK to edit a correct answer for fullness instead of answering?
