I don't have any experience with the laravel bug you referenced, however if you wish to change your app key, you will get MAC is invalid errors because items that are stored in the system database with two way encryption use the app key for that encryption.
You can resolve the MAC is invalid error by deleting any service configurations that have stored credentials from the database, as well as any private lookups. (These are the only items in the DB affected by the app key change.)
For example, sql service configs are stored in the table sql_db_config
Go in and set the username and password fields for these to NULL.
After you change the app key, you can resave the credentials.