I want to display the hardware ID when the option "Application only runs when registered" is used.

If you check the option "Application only runs when registered", WinLicense won't start your application at least that a license is present. If you just want to display the Hardware ID, you can just go to the "Customized Dialog" panel and edit the MSG_ID_LICENSE_REQUIRED_RUN and insert the string "%machineid" anywhere within your message, so it will display the current Hardware ID when the message appears asking for a license appears. Example for the customized message:

"Sorry, this software requires a key to run. Your current Hardware ID is %machineid"