After I rooted my EVO 3D I wanted to install a custom rom. I searched for hours but could not find out how to change the HBOOT version. To flash CM10 you have to downgrade to HBOOT 1.5 or lower. I was on 1.58 so it would not be compatible. To be able to do this you have to be rooted, have 4EXT recovery and have S-OFF. Also you need to have a micro sd card and a way of deleting a file off it from another device. If you have a micro sd to full size sd adapter it will work fine.
Just get an adapter like this and it will work. This one came with my sd card when I bought it.
Once you have all this stuff download the HBOOT version that you want to flash to. I will include download links in the bottom of this post. Rename it to PG86IMG.zip and copy it to the root of the sd card. To copy it just copy it like you would copy and other file. Then turn off the phone completely. and hold power and volume down to go into bootloader mode.
Make sure that is says S-OFF like in the picture below. This is required. IF YOU DO NOT HAVE S-OFF DO NOT FLASH THIS FILE. if you do have S-OFF then when it scans the sd card for PG86IMG say yes to update. use the volume buttons to move up and down and press the power button to select. If it doesn’t scan for the zip file then just press power to select bootloader mode and then it will.
Once you flash the zip file then turn off the phone. Put the sd card into the adapter and use a laptop (or any other device) to delete the PG86IMG file. Then go into recovery and flash your rom. This is one of my first posts so it may be kind of hard to understand. If you have any trouble just leave me a comment and I’ll try to reply as soon as I can. Also I have to say that this stuff worked for me but there is no guarantee that it will work for you so it helps to have a understanding of phones and rooting before trying this. I had no troubles but just like anything else that involves flashing a file this has a possibility of bricking your phone.