Is it safe to change the default font with out the boot loop of death?
It shouldn't. I use Android Font changer from the play store. But I would always still make a nandroid backup first, if you can.
If u do bootloop the rise ( this is my second one ...previously bootlooped the first because of a font i installed) how do u flash the nandroid backup with a locked bootloader
Ahh yes, that is the question. My experience is only with phones with unlocked (or unlock able) bootloaders just for this reason. For the readers as well, an unlocked bootloader means you can install a custom recovery (if one is available for your device) which will allow one to do a nandroid backup. And as such, your phone can be booted directly into your custom recovery and your nandroid restored or other functions can be performed that will get you 'out of a pickle'.
I do know on the phones Motorola released after the A855/Droid 1, there was something else called a 'bootstrap' program that was similar to a custom recovery and nandroid backups were/are able to be created; however, IMHO pretty tricky and one false step and one is screwed, since the phone must boot into regular system to restore.
So with all this long answer, I guess I must say shortly that I don't really have a good answer, but gave you some info to research.
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