If you need to modify already existing framework Perl module files or DTL template files
for customizations, you can do this in the $OTRS_HOME/Custom/ directory.

Example:

  You need to modify Kernel/System/Service.pm to add an customization, copy
  Kernel/System/Service.pm to Custom/Kernel/System/Service.pm and modify it.
  This module will be used instead of the original Service.pm.

This method also works for DTL files. Just place them in Kernel/Output/HTML/$ThemeName,
and they will be used if the theme is selected.
