Assembly language is the only practical option to develop code for the ToneCore DSP Development Kit.  There is some sample code in the Unofficial ToneCore DDK wiki.

You could build a volume preset pedal by using the tap switch to cycle through six levels set by the pots, with a crossfade or bandlimited step to make it glitch free.  However, that is a steep learning curve for an effect that would use very little of the ToneCore's available DSP, and your signal will always be going through the ADC and DAC.

You might want to consider building an analog pedal instead (or having someone build a custom one).  R.G. Keen has an article with schematics for a six volume preset pedal.

Another alternative would be to find a cheap digital multi-effects pedal that can switch presets without glitching.  If you just wanted to switch volume, you could set up some simple presets with different gains.