Once the game goes beyond lvl 50 you could be given a choice to continue to pursue your prime and secondary schools of magic or combine them into a new hybrid Sorceror school.
You would then restart at lvl 1 in magic and work up while possibly staying at lvl 50 physically or getting some of your attributes ajusted down a bit . This hybrid school of magic is very powerful so the 1st level spells take 3 or 4 pips to energize.
you would need to discover how to combine your two schools effectively. Be careful you may end up with a dud of a spell or one that backfires lol.