Short answer to your question is YES, updates may change a return.

Once a return is completed Lock the return https://accountants-community.intuit.com/articles/1861755-new-for-tax-year-2017-proseries-return-loc...

Always have a backup, or two or three or ... The data is nowhere else other than on your machine. Consider purchasing backup software e.g. https://www.pcmag.com/roundup/226992/the-best-online-backup-services

I like to keep pdf copies of returns for every completed return. There are many ways to keeping these from making folders on your computer for each client with sub folders for each year to commercial software like DMS or one of these https://www.betterbuys.com/dms/