For the drop down field, have a On Modify Script Trigger that refreshes the object (or whole layout) whenever a new value is selected.
On your layout you have a global field in that table formated as a popup list with a value list assigned.
That global field is used as a link to create a TO with another table and that TO is being used as a portal on your layout.
If this is your design then the portal should refresh when you change the value in the popup.
The trick is to use the global field as the linking field for your TO/portal.