I’m afraid I have to contradict this. In general in Node-RED, when you use the node UI, those settings override whatever may be passed along in the msg properties. In recent nodes this is often made much more explicit.
One way to make this explicit is by having a dropdown where you can choose to use the variable msg input, or a specific other option (for example, the ‘Output format’ in the ‘email content’ node.
Another way is by using a typed input field in the node UI, where you select either a specific msg property, or a text string, or some other variable.
The msg.managedFileId property is truly a special case, as the datamapper node is explicitly set to prefer any value that comes in from that property.