I've not seen a way to do this easily. You could potentially locate and hack the CSS (sorry I don't have access to a server currently to try that one out) but that would most likely not be a supported config. If you search the forums and/or the internet you'll find various attempts by people to change icons etc to white label or customise Qlik Sense. Alternatively you can effectively build your own Hub like web page using the APIs to meet your own specifications..
.png "Luminary Alumni"){kind=icon}
