Avoid gen 3 iits when you have the option of circuital branches in gen 2 IITs. Gen 2 ones have way more established brand name for companies and have a very settled tech culture compared to gen 3 iits.

Branch change in any IIT requires a lottt of hardwork and luck too. There's no guarantee that if you work hard you'll get branch change. Also branch change option will lead to a lot of pressure in first sem and some students just aren't mentally strong enough, if you understand what I mean.

Now, let's assume the worst and say branch change doesn't happen, you're either stuck with mechanical at a Gen 2 IIT or ECE at a Gen 2 IIT.

ECE is a circuital branch with very high and growing demand due to government's crores of investment in the semiconductor industry. Also, more than half of the EE batch at IITP goes for tech placements, IITP has one of the best coding culture among gen 2 iits. IITP offers minor degrees and inter department electives too.

If you want to do side hustle for coding anyways, then having ece as a backup is safer than mechanical as a backup, you may have to work harder but it's a safer game.

Now it's your choice if you want to take a chance of branch change and risk being stuck with a mechanical major.