Yes, of course. Please try opening the License Key Storage by navigating to the Help section -> License Key Storage on the Viewer's toolbar. In the opened key storage window you can register your Viewer by drag-and-dropping your license key to the storage window or by locating the license key file manually.
Yes, in order to register Viewer for Mac/Linux you need to use the license key for the latest version of Remote Utilities 126.96.36.199 (i.e. the one that is stored in the *rlicense format file). However, I'm gad to hear you've already figured out the issue and was able to register your Viewer for Linux!
Is there only the Beta viewer for Remote Utilities for MAC. The trial has expired and I have not been able to find access. The message I receive notes the trial has expired and to update license key in License Key Storage but I have not been able to find a way to do that step.
Please note that we've already updated Viewer for Mac/Linux and the latest version 1.0.10.q Beta 10 is available for download on this page. Please note that the licensing in the latest version works the same way as in Viewer for Windows, i.e. you can use Viewer for Mac/Linux in trial mode for 30 days after which you need to register your Viewer with your license key as described in this tutorial. You can either use your existing license key that was already used to register Viewer for Windows or, in case if you don't have a license key yet, you can generate a free license key using this form.
Currently we hope that to release Host/Agent for Mac and Linux OSs within the first half of this year. However, please note that this ETA is only approximate since Host/Agent for Mac/Linux are still in development. We'll do our best to make Host/Agent for Mac/Linux available for our users as soon as possible as it is among our highest priorities.