Changing SD card. Just copy everything off it, and stick it on the new one.
Launcher .dat, just download the latest and replace it.
Emunand can be dealt with one of two ways.
Just use the format emunand option again, let it create fresh, make sure you see gw3d, then just update as normal.
or
Extract emunand from old card using this
https://gbatemp.net/threads/emunand-tool-release-and-support-thread.359239/
Format emunand with new card to create the partition, then use the above tool to inject your emunand back in, then update to latest version.
I think if you've downloaded anything from eshop, extracting emunand will keep it. Formating and starting fresh will require you to redownload.
As always, make sure it shows GW3D in system settings before using the update option.
Thank you for the answers, ordering my new SD now and will try it out when it arrives!