If the individual is entered into the plan as a spouse/[civil]partner, the software will assume the IHT exemption, a default estate distribution of 100% to the surviving spouse/partner, and the spouse/partner's inheritance of any unused nil rate band.

If you need to change the status of this person, you will need to switch them from being a spouse/partner to an a "non-legal partner", which is the best term we could come up with for a partner who is neither a spouse nor a civil partner - i.e. some ineligible for the IHT exemption and Nil Rate Band carryover. 

To change a partner's status, go to the People screen. 

Select the person on the People panel, to the right side of the screen. 

Details about the person will be shown left. 

Click the Relationship field and select either spouse/[civil]partner or non-legal partner in the drop-down list.