Alter Aeon Online Help

Keywords are:  'grandfathered spells'

Sometimes spells and skills are moved between classes, or are changed in
level.  When this happens, you might not be able to cast a spell like you
could before the change, as you might not have the levels required to do so.

To work around this problem, spells can be temporarily 'grandfathered',
which means you'll still be able to cast them even though you no longer
have the levels.  Over time, you'll gain sufficient levels to cast the
spells normally, and the grandfathering is removed.