Can I join NIFT after my 4th year of B Tech or can I join NIFT while pursuing my B Tech?

I doubt if UGC allows you to join 2 regular degrees simultaneously. However, if you're after Design Knowledge then you can pursue a Non-Degree course simultaneously (even that would be tough to manage alongwith engineering for most students). There are many design based careers for the creative/ art

You can join NIFT as you complete your engineering, cause essential eligibility is minimum 60% marks in graduation. all the best:)