How to force users to change password in their first login to lighthouse?

You should be able to set the waveset.passwordExpiry field in your user form. ]

As a partial example, I tested this in the Tabbed User Form

Field name='password.accounts[Lighthouse].expire'>

  <Expansion>

    <s>true</s>

  </Expansion>

</Field>

This will automatically set a newly-created account to be expired.