I have the gauge from the 7.3 webinar and want to change the track to different colours and scales etc. I have managed to replicate the track with a couple of circles using the “difference” tool (not sure if this is the correct method but it works) but what I cannot do is paste anything into the container that holds the guage. I never get the yellow highlight around the container. If I drop a new container on screen I can paste into this but not the one that comes with the guage. Am I doing something stupid??? 
You can’t add stuff to a grouped object. There is a slight difference between a grouped object and a container. Just select the gauge and ungroup it. Once it is ungrouped you can make any modifications and then group it back together.
You can also double click or select any component or path inside of the gauge to modify their properties.
Just managed to work it out - you cannot ungroup the gauge until you remove the bindings from the needle and dig display as their bindings contain reference to “gauge”. Having done this I could ungroup and edit. Wrong or right it worked for me!
You can also add a component to a group by copying the component, double-clicking on a component in the group (this makes the outline of the group red and it behaves like a container) and then pasting your component into the group.
Just an fyi - it seems that you can’t add a component to a group (as Robert described) while using the new zoom feature. Reset the zoom level to 100% and it seems to work just fine.