The C15A uses the Cypress CY7C63723-PC USB-PS/2 Peripheral Controller instead of a PIC and it's USB which is far more difficult to reverse engineer than RS232. IIRC, you could buy the Cypress SDK for $5000 or so.
Neil Cherry and other Linux users partially reverse engineered the communications protocol soon after the CM15A was introduced but, AFAIK, nobody reverse engineered the macro/timer portion as most were writing their own comprehensive Linux applications with timers/macros handled externally.
There already is one application that runs on some tablets for controlling it - do a search here for "mochad". But, as it's based on the earlier cited Linux developers work, it also just handles command and control not downloading macros/timers.
You might find some Arduino code for the CM15A that does macros/timers - I haven't looked.