Pretty much
You should be fine to flash 4.8 over 4.6 as you described, as long as you have done an ota update at some stage in the past to populate your b slot.
Try to make a backup to inteenal storage, then tranfer to your pc until you need it, restoring should go fine from the sd card.@Beetle84. I'm currently running TWRP 3.5.0-10-0 and your Havoc 4.6. I have downloaded the 4.8 GAPPS. I tried and failed to create a Nandroid backup, and I'm tentatively ready to flash it, but I don't want to f*** it up. Hence, the Nandroid attempt. I previously installed 4.6 using fastbootd. So, as I understand your current instruction all I have to do is boot to fastboot and use fastboot to boot TWRP and flash the 4.8 zip file. Am I right? And can I then flash Magisk, etc? Can I recover 4.6 if it fails? Thanks
You should be fine to flash 4.8 over 4.6 as you described, as long as you have done an ota update at some stage in the past to populate your b slot.