I have transferred one KDE account to another. After creating the user account, do not login with that account right away. Then copy config files. Then within all config files search and replace all occurrences of
/root to
/home/username. This search and replace will work with most config files because most are text files.
Some caveats, however, is that some of those config files will contain references such as a list of most recently used files and those text links likely will point to files stored in
/root, which mortal users (normally) do not have access to. Those references need to be deleted because even after performing a search and replace, no such file exists.
Of course, as mentioned, when you copy files be sure to
chown them to the new user account.
Another option,
before creating the user account, is to copy known good config files to
/etc/skel. Then, when you create the new account those files will be copied to the new account. See if the following helps:
Creating a Nominal /etc/skel Directory
Regardless of your approach, you can experiment and try this with no permanent damage. If a copied config file fails then that will not damage anything.