Manipulate sub form link

[dynamictiger]

I have a subform which is linked on two fields, to the main form and this sort of achieves what I want. In that when I select from the combo box the form is loading if there is a matching record to display.

Ideally what I would like is the form to load at all times and if there is no match to the second child link to be in dataentry mode. I think this would include programmatic manipulation of the links but I am not sure how to approach this.