I don't know why it wouldn't work, I've messed around with spells a lot (though not sorcerer spells) and there hasn't been trouble. I haven't played in a while, but is it possible that you have more spells slots in that level than you should, via an item?
If you can't get it to work, you could use shadowkeeper to import 99 scrolls of wizards eye, only cast it however many times a day, and never cast farsight again.
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