Learning New Skills
After Re-Classing, the game allows a high-level unit to learn the new class's skills, including the base ones, for every level up. That said, it's ideal to re-class an advanced job at LV15 so he/she can still fully learn another class's base and advanced skills up to LV19. (Check out the Eternal Seals page for more information)
About Stat Activation
To calculate this, look at the current value of the required stat for the skill's activation. Let's say if a character has a Skill value of 30, the activation rate of his/her Dragon Fang is 22.5%. (30 x 0.75). If you have an activation modifier skill (Hoshidan Trust, Lucky Charm) equipped at the same time, the activation rate can be increased. Hoshidan Trust increases skill activation by 10% so in the example above, the Dragon Fang's activation rate is 25% (22.5 + 2.5).