Shotlocks are considered Major Abilities for the purposes of when they can be learned. Since most of them are Elemental, the stipulation will be that you have to have to know, say, Fire, to be able to learn a Shotlock like Flame Salvo later on. If the initial Spell levels up (Fire to Fira for example) then the corresponding Shotlock (Flame Salvo in this case) will also "level up" and be able to deal more damage than it did previously.

Also, yes, you can make up Shotlocks. But for the purposes of when they can be learned, they must always be counted as a Major Ability.

Hope that cleared some things up.