I'm working with LEDE 17.01.5. It's not clear to what booting features have made it into this release.
The small root partition is not workable for my needs and I need to utilize the /dev/mmcblk0p10 partition, but no one has reported success with pivot overly or pivot root.
Correction I have the NGB6817. 17.01.5 installs and seems to work properly, I just cannot seem to get a larger root volume so I can install more than a couple packages.
After exhausting everything I know about setting up pivot overlay or pivot root, I gave up an took another approach.
Not too concerned about having a function dual boot, I deleted partitions 5 through 9, recreate partition 5 with all the free space. After reboot I ran resize2fs on the partition and now my root_fs has ~370M.
Your custom partitioning changes will blow up badly with the next sysupgrade. The sysupgrade scripts depend on the correct number, order and assignment of partitions (at least for partitions 3-8), their size doesn't matter (as long as they're big enough, so at least 1+4+32 MB (keep in mind, OEM expects to have 64 MB at its disposal for the rootfs, but around 21 MB are already in use today)) - but header/ kernel/ rootfs and header_1/ kernel_1/ rootfs_1 must be present and at the correct location. Sysupgrade (in 18.06 and newer or stock OEM ZyXEL, just as well as OEM u-boot) always alternates between both locations.
Edit: Given how header/ header_1 are accessed (raw), I'd also strongly suggest to keep these partitions exactly at their original size.
No, it's not - sysupgrade and the OEM firmware tools rely on the same markers to determine the install location and will blow up in very similar ways. I'm not saying that you can't resize the partitions, but you must keep 3-8 present and intact, just borrow the space from 10.