I am a standard flight simmer just like you. I have no connections with Laminar Research (LR) or any other software developer or computer seller.
When X-Plane 10 is or has been installed on your Flight sim machine it should be loaded to the desktop (recommended by LR) or to the root directory of your main flight sim drive. In my case I have an dedicated drive. My computer operating system and other necessary "rubbish" is loaded on my "C/:" drive.
During the installation process the software does not migrate some of the files into other parts of your computer eg some software dumps files into Windows directories and subsequently difficult to find. What this means it is totally independent and can be transferred on a USB stick to another computer to use.
In the case of X-Plane 11, from my readings of earlier forum questions and other documents the same situation occurs for X-Plane 11 and it does not impact on your X-Plane 10 software. The rough analogy being, when both software packages are installed one is a pear and the other being a plum (refrained from saying one is a lemon and the other an orange). The same situation occurs even now with the XP11 Beta version ie fully install XP10 now and fully install XP11 beta now and XP11 will automatically upgrade to the final/official release version
The short answer to your question is yes and is permanent provided you install each version of the software independentlyonto the desktop or as in my case it will be E:/ XPlane 10 or F:/XPlane 11.
At this stage, X-Plane 10 can still be purchased on its own for download. Latest version is 10.51. LR is also offering XP9 for those who are interested.
Hope this helps. Good luck.