The Influence of Levels on Actions and Cross Class Skills

[Coglin]

All traits will be made class-exclusive.
Adjustments will be made so that certain actions will only unleash their full potential when paired with traits belonging to the same class.

If it helps. My interpretation of this is that spells/abilities used cross class will be scaled down do to the lack of the class traits that are non-transferable to other classes.

thus in my understanding it would scale, but not to the same strength it would on the original class. I don't believe the spell itself is level related, you simply aquire the spell at said level.

[Inaaca]

As mentioned under 1. Class-specific Actions, upper tier actions will be abolished in favor of scaling the potency of the base action according to level. The effectiveness and MP cost of the action will be dependent upon the level of your current class.

Does this quote not already answer the question? If you have a CNJ lvl 10, and you put Cure onto your GLA lvl 50, the spell will be based off of whatever your current class is.

So as long as you're on your GLA, the spell will be based off of the lvl of your GLA, not your CNJ.