Despite using Modx Revo for several years, I’ve never been able to find a way to set the media browser upload destination to default to (for example) assets/images. Is there a way to do this? It defaults to the root which is really annoying for some clients.
Sure there is. In the manager go to media > media sources > filesystem. Fill in the basepath & baseurl with your path (assets/some/folder/).
I always setup a separate media source called “clients”.
And I thought this was deprecated because of the message in the file system. Thank you!
Well it appears that this isn’t that simple. Doing that broke all links to images.
Maybe a link rebuild is needed? 
Manage > Clear Cache > Refresh URIs
I’ll give it a go and report back
That’s correct. It is advised to start with this before you enter content. For now, you can go into your DB and search and replace the paths with 2 clicks.
I’ve got it eventually. Refresh URIs was certainly needed but I also needed to associate the relevant TVs with a media source. It certainly looks like good practice to always set this up so I’ll always build it in, infuture. The only thing I can’t figure out is why the client can’t see sub-folders of the media source when set to anything other than a Sudo User.