So when in an assembly on the browser in modelling if you right click on the derived part there is no open option like right click on everything else you can double click it and it opens but this is not obvious as this gesture is normally edit in place. This should be added

Also when right clicking on a part within the assembly graphics window or browser you should be able to open its derived part. If it has more than one then it presents a list which you can choose which one to open.
