Can I alter data within a mariadb db using mysql-workbench?
In principle, yes.

Though it depends on the GRANTs for your particular database user. If you can't change the values, then try another database user or create a new user with the correct GRANTs.

You should be able to click on a table to list its records (it's the right-most icon when you hover over the table in my MySQL Workbench version), then double-click on the value you want to change, change the value, then hit the 'enter' key on your keyboard, then click the 'Apply' button below the table listing.