The cross pin in the bottom of a S&W revolver does not need to be removed. The U-shaped stirrup is just sprung apart and lifted off it.
Now, Colts are a whole other story. Lots more work to install the Monogrip and you have to replace a pin, IIRC, prior to again installing any factory grips. At least that is the case for the D-frame Colts.
Bart Noir