Sounds great.
Back up all your pictures etc before you do *anything*. At some point in the process this phone is going to get wiped totally clean, whether it's part of HTC's repair process or you do it first, intentionally or unintentionally.
Just one last reminder, if you flash that custom HBOOT, now you *really* have a good reason not to go S-ON: attempting S-ON before reverting to a stock HBOOT will kill the phone for real.
If for some reason HTC attempts to S-ON while it is in their possession, well, that's going to be one confused technician who has to figure out how to get you a working phone.
Not sure if you caught my post a couple pages back where someone over in the ARHD thread says HTC (when deciding whether or not to even accept the phone for repair) didn't care about S-OFF but they *did* care about an unlocked bootloader. (Side note - it was returned S-ON.)
Which brings us back to the part about backing up all your data: if you change the lock status of your bootloader, that's going to wipe the whole phone, so save all your precious stuff *before* you even start messing with the phone.
Sent from my HTC One using xda app-developers app