I usually only change the title if I wrote a post with a year in the title (2015 articles would be changed to 2016) or if I re-optimise the article for a different keyword and I've never noticed any negative effects when I do this.
As for changing the URL, I try to avoid it when possible by planning ahead (e.g., the article with a year in the title will not have the year in the URL), but when it does happen, I 301 redirect the old URL to the new one. I've had to do this twice when I added HTTPS to a few of my sites and another time when I re-organised the URL structure of another.