Are you talking about a docker setup? if so, yes, as long as you update your bind mount to the new location. If manual install, I would think that you'd have to either leave it in place or find what references that location and update it as well.
Themes would be my start, but that would require the instance owners to add them once created.
There is the Lemmy Instance Admin Chat: https://matrix.to/#/!OwmdVYiZSXrXbtCNLw:matrix.org?via=matrix.org&via=aria-net.org&via=40to.ca
On my instance at least, spinning on click normally meant issue with email submission. But there wasn't any good feedback like "failed to send email"
Though, I do still need to figure out why images aren't loading... source
I did it! I got my instance up and running. I had to still create the pictrs folder and chown on it to get pictrs to work. And then after that, it was just doing Nginx Proxy Manager and some config in my hjson file. https://www.pastery.net/rpmppa+tdqrrx/#rpmppa