Some one has already cast a global enchantment . Can I cast the same spell again?
(I think the answer is no , but I heard some one talking about stealing a global enchantment with superior gem income.)
yes you can if you beat it in gems + random roll. Is used the dispel mechanics, check the manual for the specifics.
One note, boosters for items do not give a bonus if you go over the required path. Only natural levels. (Also, if you get to the minimum casting level using boosters, you do not get a malus).