EDIT: the pdf had a wrong explanation of how rumble profiles work (thx to Saemon No Jyo for spotting that). I've ninja-updated the 2.2.6 zip with the corrected pdf. The relevant part is this:
- _cogacc_rumble_map0/1/2, _tireslip_rumble_map0/1/2: each map is composed of 4 floats representing the two interpolation points translating the source value into a rumble value: [min driving value, max driving value, min rumble strength, max rumble strength]. E.g. for tire slip "{0.04,0.10,0.20,1.00}" means that at 4% slip rumble will be at 20% and at 10% slip rumble will be at 100%. You can modify the maps in the .ini file manually.