If you are just experimenting, backup your customizations and try whatever you like. As long as nothing touches the U-Boot partition you should be able able to revert with the aid of serial and USB or wired ethernet.
If you are making something that needs to be consistent, then you need to be building from source with the ability to control which specific improvements/alterations/breaks of things that used to work go into the configuration you use.
@Brad-Buskey some similar systems offer an ability to download a backup file through a web gui as part of the sysupgrade functionality but I don't know if this is one of them.
Speaking generally rather than about the omega 2 in particular:
If you already have the read-only system image corresponding to your current state (for example from the download server) then all you would really need to backup would be the mtd patitions containing the "firmware" identity data (possibly), and the one containing the jffs overlay that captures any changes you make on top of the read-only core.
Approximately speaking, if you boot in failsafe mode you could dd the partitions (probably /dev/mtdblock2 and /dev/mtdblock4 but I don't have a running system here to check) to /tmp and then download them with something like scp. It may also be possible to directly scp the /dev/mtdblock psuedo-files, or possibly to pipe the dd copying through gzip to make a smaller backup.