I recommend not RMAing cards for fans.
I recommend busting the power supply side instead.
A lot more work to check the bios when the card doesn't power.
I agree with you that you shouldn't RMA it for something simple as a dead fan because you can just simply re-oil the bearing yourself or buy a new fan on Aliexpress and swap it out. Since you have to pay for the shipping for the RMA, the cost will be equal so in this case you are better off just buying a fan rather than going thru the warranty process.
I wouldn't recommend damaging the GPU however. These days GPUs rarely have exploding MOSFET or Capacitors and if you do it on purpose they would know very easily and you would get blacklisted since its highly illegal doing so.
These RX 470's are so cheap these days that if one is completely dead just buy another one for like $75 on eBay. Not worth going thru this huge hassle.