Re: Please help me understand
Which is why you give the character a limited VPP. You can place limits on how/when the spells can be changed, add on Requires a Skill Roll, which also requires the character to have the skill...
Also, have all possible iterations of spells fully written out prior to play, like the week before. Someone with little experience wanting to change on the fly to something not statted prior is a serious game disruption.
Normally lasts how long? A week? -1/4 at most. Less than that -0
The spellcasters I've done are high-end, do it on the fly, VPPs.