Meditation and 'not trying to change anything'
Yes. You are not trying to do something through you are doing it with a objective relieve your stress.
If you try there is a possibility of subtle craving. If at all you are changing anything is to calm your fabrications and tame your afflictions.
However, in my practice I have found that if I consciously try to relax during a session (muscular tension is an issue with me) it can be a much more fulfilling, refreshing experience. Is this not an example of trying to change something, and therefore 'bad' practice?
If you generate any anger or aversion towards this feeling or any liking towards another state or wanting something else then it is bad. Otherwise it is good. Relaxing means you can:
Also see: What is Mindfulness? What are the 6 Rs?