Yes....It is harmful to change the content every time for SEO. Because the Content is the base of SEO work.. If your page rank is not good or you want to change your content then you can do it for one or two time it is fine but every time to change your content is harmful for your website.
Editing content on your web pages should not be a bad idea if you feel that the content is bad on the other hand changing content at least once a month is also good, probably you did not have a video.. images etc these can definitely enhance the look and feel of your website at the same time they will also help in your SEO.
For seo then probably Yes! ... As a matter of fact the website needs to be updated according to own requirement like if you have got ecommerce website and you update prices, product description etc. that is normal but manipulating website content just to get caught by crawlers isn't good practice.