The D-Fend project is discontinued and so it won't take advantage of the new features of new versions of DOSBox, and additional problems might also arise. You could migrate to
DBGL whose interface was inspired on D-Fend's but it's active and updating, and it will import your D-Fend profiles for you.
In order to backup your profiles, either in D-Fend or DOSBox, to restore after resintalling, you must safeguard certain files and folders, to CD, USB, or whatever you prefer. I don't have any installed so I can't tell you which folders, but if you're not sure just backup the whole folder where the program is installed along with all its subfolders.