Memory tome for KP and an item for CP are completely different situations. KP is limited, you have at most 75. CP on a class can be accrued even if the class is maxed. Although some moves on certain classes could be left at level 1 for the sake of conserving MP, there's some value to level every skill as far as I know. So if the point of resetting CP is to reuse what you used on a "useless skilll," then as Katashi said, just get more. Re-leveling a class is a waste of time, as well as spending gold/AP for such an inefficient use of resource. If it's to keep skills for Mp conservation, you should have an illu handy (plus there's no skill you would be spamming that doesn't benefit from having a higher level).