@Jtjumper Yes, you can copy your epub to a different folder on your PC. In fact, you can even download a second copy for your phone or tablet and can convert the epubs to a different file format and upload them to your e-reader for personal use.
According to the FAQ:
"Premium ebooks you have purchased using Coins can be downloaded from your library as often as you'd like, and the files are yours to do with as you wish."
"You can convert them to other formats and save them to any device you own".
What you can't do is share the epub or it's artwork. According to the Terms of Service:
"For the avoidance of doubt with respect to any Premium Content that you purchase or access via the Site or Service, such content is only made available for personal and non-commercial purposes. The delivery of any Premium Content to you neither transfers any commercial or promotional use rights in the content to you nor does it constitute a grant or waiver of any rights of the copyright owners in any artwork embodied in the content."
Also the terms of service make clear you should download the epubs as a backup in case JNC ever have to remove an ebook (e.g. if their licence expires), etc:
"Disclaimer. J-Novel Club does not guarantee that any content (including without limitation J-Novel Club Content) will be made available through the Site or Services, continuously or at all. WHILE J-Novel Club IS UNDER NO OBLIGATION TO DO SO, J-Novel Club RESERVES THE RIGHT TO REMOVE AND PERMANENTLY DELETE ANY CONTENT FROM THE SITE OR SERVICES WITHOUT NOTICE, AND FOR ANY REASON J-Novel Club DEEMS SUFFICIENT."