My paper's content is slightly changed from the abstract I have submitted to a conference, can I edit the accepted abstract on my poster?
I work in astronomy.

I have never heard of anyone in authority at a conference complain about a slight deviation from a submitted abstract. 

I suggest writing your poster on your new direction, with a corresponding abstract.

I would also submit your amended abstract to the LOC of the conference as soon as possible. Mention that your work has taken a slight turn but the main topic and co-authors are unchanged. 

If there is time, the LOC can include your amended abstract on any web-page or hard-copy documentation. Apologise for the inconvenience that this may cause the LOC and ask nicely that they make these amendments, if possible.

Even if these documents cannot be altered, I doubt that anyone is going to get upset that your new abstract is not exactly the same that you originally submitted.