The support on the forum is usually pretty much excellent. You will note over time that the actual developers answer many questions on the forum, and get involved in discussions. Plus the owner and CEO of the company. You won't get much better access to company resources than that!
A Licence Restore is a way to recover your licence if you lost it. Usually you don't use one of those up with a new installation, because JRiver installs a licence on the current PC when you purchase, if it finds an installation of MC. JRiver also sends you what you need to install the licence when you purchase in an email. But I think if you use the method of entering the Registration Code into MC, it does run the Restore process and send you a new email.
The mjr file contains your licence information and allows you to install a licence to any of your PCs for up to 14 days from when you receive the email containing it. If MC is installed already, in Trial mode or Licenced, when you double click on the mjr file it installs the licence into MC directly. So for example, you may wish to install MC on two PCs. The first PC you did the purchase on is licenced during that process, then you install MC on another PC, copy the mjr file to that PC and double click on it, then that second PC is licenced.
It's all in the stickied posts here:
https://yabb.jriver.com/interact/index.php/board,56.0.html or in the Wiki:
https://wiki.jriver.com/index.php/Restoring_a_LicenseLearn to search both the forum and Wiki for answers. You can search directly in either, or search everywhere using the custom Google search, here:
https://www.jriver.com/support.html