Afterwards are changes of the questions, sometime seemingly slight, does a change counts as a break?
I think it was right (skillful) of you to post this comment ...
(Maybe) Better to put your update into a new question because it would confuse everything. Maybe Beginner like to answer this question independently.
... instead of letting the OP edit their question after it was answered.
Some other Stack Exchange sites have strict rules, like,
- A question must be valid (e.g. clear) otherwise it's closed until it's clarified
- A (non-closed) question that has been accepted and answered cannot then be modified, if the modification will "invalidate" existing answers
On this site, the community wants/wanted to be less strict about accepting or closing questions, so we have a very liberal (permissive) policy about not closing questions, and people sometimes answer questions which aren't clear.
What are ones reasons willing to change answers, questions, delete parts, modify... afterwards if it is unskillful?
I sometimes edit other people's answers, to improve the formatting, grammar, and spelling (to make them easier to understand). I don't think I try to change the content of other people's answers. I sometimes delete or reword (soften) a fragment of an answer, if I think that fragment seems hostile.
I tend to edit (add to) my own answer, if the OP edits their question, or if the OP posts a comment which asks an additional question.
How to go beyound such problems, what whould be a secure solution?
I suppose theoretically we might lock or protect questions so they can't be edited after they're answered. But I think that would be too rigid a policy, because instead I think it's good to clarify (improve) questions, just as it's good to improve answers, especially if it remains our policy to accept (not close) slightly unclear questions.
I suppose we should (and maybe usually do) try to draw the line at asking a completely new question. If the OP has a new question or a follow-on (subsequent, related) question, that should be posted as a new question (or perhaps as a comment under an answer, asking to clarify that answer).
Instead of a "secure" solution (automatically making questions read-only) maybe have a human or humane, flexible or responsive solution, which tries to provide appropriate responses on a case-by-case basis (e.g. the comment you posted when you decided that changing that question would be too much of a change given the existing answers).
What are the consequences of missinterpreting
I suppose a consequence is that the Q&A is less useful than it might be.
We shouldn't lose track of the fact that the Q&A is meant to help the OP and other readers. And I think it's meant to be primarily helpful to the OP (who asks and maybe revises the question), so I'd hope for a solution which doesn't make the site less usable for the OP (in this case I hope that asking the OP to post a new question might have not hurt anyone). But always locking a question, never letting an OP clarify their question, seems to me too rigid.
it should not be taken as meta
I think you don't like Meta for some reason.
On the other hand some users (perhaps most users) are uninterested in discussing how the site is run, and topics about the site (especially if the site consisted, mainly or mostly, of topics about the site) are uninteresting and off-putting.
Moderators generally do and will continue to move topics about the site, the site's policies, and how the site should or shouldn't be used, to Meta.
Make use of "on hold" and possible protection of question
I think that's going too far. But I could try to do it, if a lot of people agreed on it (e.g. if several users agreed on Meta that it's a necessary and desirable new policy).
notification of answerers in cases of question changes
The current software doesn't support that feature.
A programmer could possibly write a user script (a "stack app") to check if questions are edited after you answer them.
That job would be more complicated for you, because you have about half a dozen user accounts.