You need root capabilities to use loadkeys. It is common to set the setuid permission bit on loadkeys. Setting this bit will cause any processes spawned by executing the loadkeys file to run as the owner of the file (usually root).
For added security, you should change loadkeys's permissions to 750, make a group for it, and add any users that need to use loadkeys to that group.
$ chmod 4750 /bin/loadkeys # setuid, group- and user-only read and execution $ groupadd loadkeys # you can use any group name $ chgrp loadkeys /bin/loadkeys $ chmod 4750 /bin/loadkeys # setuid, group- and user-only read and execution $ gpasswd -a user loadkeys # add user to the group