can i give my 12th through gujarat board again even after passing my 12th from mumbai
According to Indian Supreme Court, there's no specific rule that can prohibit one person from giving two same examinations . If you want to qualify for your boards from two different states, please try to register with a minimum 1 year gap.
It is also mentioned in Indian Law, that is if a student is caught appearing for two exams in the same year, he/she can be suspended from appearing in any type of exam for atleast next 3 years.
So be careful.