We strongly recommend to complete the configuration of the participant registration module before you open it for attendees, but you can add a special participant group with a registration code for a discount at any given time, including after the registration phase has already started.
 
In this example, we use the same code (or code pattern) for all participants of this particular group.

You need to create a new participant group for the discounted fee and define a registration code pattern for this group.

• Please go to: Overview => Settings => Manage Participant Groups
  Create a new group for the discounted registrations. While editing this group, define a code or code pattern and enter this as "regular expression" (see screenshot). You find some examples below the field "Regular expression to verify code (for experts)".
  Participants will have to enter a code matching this pattern during registration when they opt for this group.
  Example: "^TEST123$" (without quotes) will match exactly the string "TEST123". (You can also enter "TEST123" as pattern only, then every code will be accepted that includes the string "TEST123".
  You find more information on regular expressions as well as examples here:
  http://en.wikipedia.org/wiki/Regular_expression#Syntax
  http://www.phpbuilder.com/columns/dario19990616.php3
  http://www.regular-expressions.info/
  
• Enter the prices for this group and for all relevant price categories
  Please go to: Overview => Settings => Prices
  
• Enable the option to ask for a special code for the reduced fee.
  Please go to: Overview => Settings => Base Data for Participant Registration
  In the section "Participant Registration", choose "Yes, but show field only if required for the currently selected participant group" or "Yes, always show input field" for the option "Ask for a member number/ matriculation number/ special registration code?".
  Click on "Edit phrase" in the same section to change the wording to fit your needs.
  

Please test the new settings.