Recently I change my server to a remote host. That's means all my work there I used Postgis layers, the host name at the source is set to 'localhost' and I need to change to 'remotehostname'. The content of the source appears with the complete connection, host, dbase, login and password and the query with, at the field "source layer" at general tab in the layer properties. I can select copy and paste, but this field can't be edited. There is a way to edit this source?
You can open that QGIS project file in any text editor instead and do a simple Find + Replace to change the hostname quickly.