Wizardry is the learning and use of spells by rote.
Each spell is learned as a separate skill but is cast through expression of the skills used by the creator of the spell.
Creating a spell is achieved by developing a skill for that spell. The spell must use rune forms which the creator knows, and these same skills are expressed during casting, though the caster need only follow the form for the spell, and does not require any general ability in those skills. In this case the spell may only be cast exactly as designed, ie. the same number of each rune as specified when the spell is created. If the caster does possess the appropriate skills to express the runes contained in the spell, they may vary the number of any rune in the spell as if they were the creator. If the number of runes of any type is reduced below the number required for the spell to be functional the spell will fail, eg. attempting to create a sphere with a single Shaping rune. The caster cannot use this ability to change the function of the spell, only to adjust its parameters, eg. increase (or decrease) the range or damage of a spell.