Well, the twrp folder structure looks like this on sdcard:
TWRP/BACKUPS/xxxxxxxxxxxxxxxx/folder_containing_the_backup
The x's represent your device's serial number (you can get that by running fastboot devices). Then within that folder you have separate folders for each backup. So essentially, you just need access to your storage and you can paste the backup folder in the appropriate location.
The easiest way to setup the file structure is to simply make a backup yourself via twrp. Then you can paste the other backup in the directory named as your serial number.
Also, you do not have to be s-off to use RUU files. They are officially signed by HTC and thus are okay. The only way they will not pass a security check is if you are trying to downgrade anything (bootloader, mainversion, radio, etc.). So you have to use one that's ≥ to your current build.