Spot on Dennis; in Cakewalk I only embed expression commands into tracks to adjust the relative volume. The track volume is used to adjust the overall level of the track within a mix.

Regarding volume pedals, you can get mono and stereo units that are designed to be in the signal path from your keyboard to your mixer and these would almost certainly not operate correctly if used as an expression pedal plugged into an "external controller" jack on a keyboard.