Stop all SQL services, then go into SQL Server Configuration Manager and select SQL Server Services in the tree. Then go into Properties for the database engine service of interest and select the Advanced tab. Click the dropdown arrow on the Startup Parameters value, and add ;-m (semicolon, dash, m) to the end of the text. Click OK to exit the dialog box. Restart the service for the SQL instance of interest.
If you have SQL Management Studio open, close it and then right click on the program and select run as administrator. Fix the Security options you need, save and then close the program. Go in SQL Server Configuration Manager and stop the SQL instance of interest and then go in and remove the ;-m from the Startup Parameters. Restart the SQL instance of interest and start SQL Management Studio(without running as administrator) as the user or user of the group you made changes for and ensure the changes you made worked. If so, restart all of the other services needed to bring the SQL server online.
Props to Jon Seigel and Glen Robson for this solution