Is changing post from category in a large blog a good practice?

Unless the permalink structure has category in it, changing category won’t give 404 as the URL will be the same, and just content of category pages will change.

If you have date format (year/month/date) in your permalink structure, then changing the date of the post, will break the link and will return a 404 but I think you can easily do that (if you need to) and manage redirections with the help of this plugin (it will search on a 404 and automatically redirects to the right post found, works very good in case you change permalinks, so I think it will work pretty well here too) http://www.microkid.net/wordpress/permalinks-moved-permanently/