Saving Changes Is Not Permitted
Bradley Schacht is a Principal Program Manager on the Microsoft Fabric product team based in Saint Augustine, FL. Bradley is a former consultant, trainer, and has coauthored 6 SQL Server and Power BI books, most recently Learn Microsoft Fabric. As a member of the Microsoft Fabric product team, Bradley works directly with customers to solve some of their most complex data problems and helps shape the future of Microsoft Fabric. Bradley gives back to the community through speaking at events such as the SQLBits, Fabric Community Conference, PASS Community Data Summit, SQL Saturdays, Code Camps, and user groups across the country including locally at the Jacksonville SQL Server User Group (JSSUG). He is a contributor on SQLServerCentral.com and blogs on his personal site, BradleySchacht.com.
This is a less that optimum message to get. No one wants to re-create a table every time you need to make a change. Luckily there is a fix. In order to get around this message you can change a setting in the tools menu. Simply go toTools > Options > Designers > Table and Database Designers. From there uncheck the box next to "Prevent saving changes that require table re-creation" and you will be able to edit your tables without issue. 
You will still get a message that tables are going to be affected by the changes, which is fine, as your changes will now be saved! Remember to always be careful when editing your tables.