Deleting default setting

Dear Gurus,

i would like to know if is possible to delete a default value setted from procedure.

For example i have the following procedure (for multivalue Characteristic).

$SET_DEFAULT ($SELF,SP01N , 'A')

With this syntax i get the value default, but the user is able to change but no to clear the default value.

How i can clear the value ? I have already use $DEL_DEFAULT ($SELF,SP01N , 'A') but in this way i delete immediately the value and not after the user valutation.

Thanks a lot

Daniele