LEDE? It's a comlete system with bunch of packages. You can do what You want - it's clean Linux. If there's something missing, You could write Your own program/package/script. It's flexible and open. And that's why You need as much flash as possible to avoid extroot.
If You use minimal image even 8MB flash will be enough, but try to use more services, install packages and popular 16MB is not enough.
As routers're going more and more powerful why should we be limited to basic services? Todays routers are like servers in not-so-far past: compare R7800 to i.e. basic Sun SparcStation II
@avx seing that it worked for you, i've done the same and yep it works nicely. I've also restored the mtdblock backups @Wally recommended doing prior modifying the DTS to see if i could go back to OEM firmware and it also works.
I find @hnyman's build very interesting, and i think i'll stick with this one.
Wally mentions writing the partitions back from backup to return to stock but I found a simple tftp flash to stock got me back and my settings are automatically restored, so no need to setup up again in stock firmware. But yeah, still best to keep a backup of the partitions in case something goes wrong or gets corrupted.
TFTP always work - this is the beauty of R7800 You can't softbrick it. You can flash OFW without restoring backup, it will work but some things could be missed, I didn't tested everything but looking at partiton dump I saw some strings related to languages, settings etc. I suggest restore to get state as before modification. Just in case.
@dissent1 you're right, but it's true only if You dont use storage (any kind). So flash modified, check, flash OFW, check. In any other case when You use storage You don't have any control where data is written (phisical sector): it could be written on begining or in any place that was marked as less used. So if You want to mitigate problems, always restore orginal (removed) partitions from backup before flashing OFW. Just in case...
I made some changes to partition layout (on 18.06) - I've removed netgear and reserved partitions. Looks like second one contains some language files for OEM interface but if I remember they are downloaded after first login. of course I made binary backup of these (in fact all mtds) partitions.
ah, i was wondering about that. unfortunately the D7800 that i have access to is in my parents' house on the other side of the world (literally). even sysupgrade is a bit of a fraught experience (did not add my cron scripts to reinstall openvpn to the persisted config, and i forgot about ddns anyway), cannot imagine trying to get mum to TFTP upgrade it will be very practical !
That would be something for you to find out, it depends on the OEM partitioning, what's going to be lost when resizing partitions and if the OEM firmware can still recreate the overwritten bits and pieces. You will need to get very familiar with contents and purpose of the relevant partitions, find out how exactly the OEM firmware behaves in the absence of its expected contents there - and then determine if something like that might be safe to do, or not.
The only safe answer is 'no', for any other answer, you have to do the digging and development.