Here's the trick. That works well. When I saw it working, I say Wow! :)

From the opener in the icon field which is used to call a pick list to select a member:

...A HREF=javascript:AssignationMember(document.FournierTransformation.NoMember)

From the opener, the AssignationMember() javascript function:

loField=''

function AssignationMember(toField)
{
   window.open("MyUrl");
   loField=toField
}

Then, from the called window:

window.opener.loField.value=lcMessageMark