Naw, not complicated, and it's how I do all my brass buttons when I'm too lazy to remove them. Brings surfaces to fine consistent luster.
Using blue painters tape, cut a few thin strips to mask between and around the buttons. Doesn't have to cover all around the button like you were masking for paint, just enough to keep the pad fibers away from the anodizing where it does show through. Then mask the entire button side of the mod, placing the tape widthwise, not heightwise.
Put a medium (maroon) metal finishing pad on a flat surface. Holding the mod button side to the pad, move it gently and steadily in a straight line, using very little pressure, the length of the pad and back. Check progress, making sure none of the masking edges are lifting up. Repeat until you like the finish. Can't recall exactly, but the brass should look totally fresh in 6-8 strokes.
One thing to be aware of. The pad will impart its own fine grain to the finish, which will be crossing the rougher circular machine marks of the big button surface. Still will be a vast improvement over tarnish, but if you think you might not like that don't do it by this method. Instead cut a small swatch from the pad and work the buttons with your thumb in a circular motion. Personally, I prefer the more consistent look of the linear method.
3M Painter's Tape, Multi-Use, .94-Inch by 60-Yard - Painters Masking Tape - Amazon.com
Amazon.com: 3M 7414NA Hand Sanding Metal Finishing Pad, 4.375 in by 11 in, Maroon, Medium: Home Improvement