Unfortunately not, you need to do a clean flash in this case. You can only dirty flash if you previously had my unofficial build installed.first of all, I'm amazed of your work. I'm very pleased to see older LineageOS is still in develop somehow.
second, is it possible to dirty flash from official LineageOS 16.0? my build is the last nightly zl1 for LEX720 (2020-04-18). I'd strongly stick with my /Data, so avoiding to wipe /Data partition is a must.
considering Flash Instruction, would it work just wiping /System and Cache+Dalvik before installing this build using TWRP?