There would be no problem since he is studying in CBSE schools.

But if he writes an engineering entrance exam
At the time of counselling his state would be according to birth certificate.

If he was born in Ap and wrote exams like EAMCET he would be having advantage of getting good colleges.
If he was born in TN and wrote EAMCET he has some disadvantage.

Hope it helps.

Thank you :)