The abra_db is pretty straightfoward, it explains really well how it works.
// Hocus-Pocus (Abracadabra) Castable Skills Database
//
// Structure of Database:
// SkillID,DummyName,ProbabilityPerLvl
//
// 01. SkillID Skill ID to be casted by hocus pocus.
// 02. DummyName Name of the skill (informative, not used by server).
// 03. ProbabilityPerLvl Not a rate! Chance at which the skill is selected compared
// with other entries probabilties
//
// NOTE:
// - The skill is picked at random from the entire database and then tested for rate. If it
// does not succeed at that rate, another skill is picked and tested. This continues
// until a skill succeeds. Abracadabra-specific skills have a different chance to occur
// depending on skill level used. All other skills have an equal chance and appear from
// level 1 onward.
// - To remove entry by importing, put "clear" (without quotes) in DummyName
In short, it's not set as a percentage, but in 'tiers'.
For your best luck it is for the best that you pick a skill that appears as much as you wanted 'Class-Change' to be casted and copy its values to it.
Abracadabra specific skills has different chances by skill level by the way.