In Astroneer is it possible to rotate an object? Like I've added a printer to a platform can I just unplug the platform and rotate the object? Or am I just missing something here?
Yes, it is certainly possible. You can look in your settings for the key. For me the key is Z or X. If you press F1 and look at the 5th help page, there is an explaination on this feature.
The name of the key binding to rotate left is 'Context Left', for right it is 'Context Right'.
Edit: As of the full release of Astroneer, the standard key bindings for rotating are C and V.