LAST EDITED ON Dec-07-01 AT 12:11 PM (Pacific)Go ahead and change him you don't lose anything mage-wise,
you still have all the mage capabilities you had before the change, except you do not have the 25% bonus to the mage skill.
And once a bishop you can still get the best mage spells by level 18(all together 7 bishop +11 mage), plus you will now be able to begin learning priest, psionic and alchemy spells starting at level 1.
Some posted a more thourough answer to this question.
So for a mild spoiler(in that it gives some info on how the game works and not an ingame event)
try http://www.softwarespecialties.com/dcforum/DCForumID7/790.html#
Brother Steven