Evaluating selected row member on form...lookup an alternative value and display on another form

I have a form with an action menu that evaluates the project in a row and opens another form and uses this member in the page dimension. This works without issue. However, before opening the form, I want to evaluate the member selected and lookup up a corresponding project member in the same dimension and display that member on the form. Using Groovy to perform the lookup is the easy part. The issue I am having is evaluating the member chosen and then forcing that value in the page dimension on the form and implementing groovy to