is it safe to change the publish date when we update a post? Will that affect SEO, if i just make some minor changes to the post and update
It’s not ok.
If you change your publish date, you will loose your age factor. Google will penalize sites that keeps changing their publication date to manipulate search results.
Changing Publishing Date while updating post is not a good practice. I tried this few months ago and got hit hard on one of the high ranking post and it taken 5 weeks+ to get back the previous position.
Instead of changing the publish date you can show Last Updated Date.