Depends on why and how frequently. Digital Cowboy (sadly no longer here) has had three covers (two AI generated - with the title Digital Cowboy Dane - by Pocket FM, the other cobbled together in Paint Shop Pro using "copyright free stock images" and Windows fonts; also had a decent one someone cobbled together and sent me unsolicited that was never used because it came through about a week before I was asked to pull it from this site).
Between Worlds (also no longer here) had four (one generated by AI and edited in Paint Shop Pro for it here, and then, as Between Earth and Pyrroth, one really bad one generated by Pocket FM, one updated one for its initial release, and a revised one that is actually pretty good now for when the contract went out).
Strange Awakening had ... well, three rejected before the current one, plus the site-generated placeholder. Not sure if that counts.
I think I changed Blood Diamond's cover once after posting, but Diamond in the Rough and my other stories all have the original ones I threw together.