Forum Moderators: Robert Charlton & goodroi
Now, if you are changing URL's this could have a negative short term effect. Old and outdated urls will return a 404 and google does not like that. If you have any outdated url's I would look into the google remove outdated link process to update the data base. Its a very easy process and google will remove those urls in 5 days. I just did it with my site and it worked out well.
Google will crawl the new url and it will take time to make it in the index. Add a google sitemap so it will make it easier for google to crawl and let google know about the changes.