If you are just aiming to fix the heart rate monitor, then yeah thats possible, just use the guide for the replacement motherboard up through step #6 and the try to source a replacement back housing/heart rate sensor for the device. If you are not able to find it, try looking for a Fitbit blaze that has a cracked screen or that won't turn on because odds are that unless the back glass is cracked, they are usually pretty good so unless you can't find a replacement sensor, your best bet is trying to find a really broken and cheap example with an alright looking back.