While a pop up window can be set up for this, you can also just format your Shift ID field with a drop down list that displays the ShiftID and also additional information such as the name or description of the shift. The user selects by this additional information, but the drop down list enters the ID number to establish the relationship. This approach doesn't require any shifting so it's simpler to implement than what you describe.
On the other hand, the more values in your value list, the more unwieldy this approach becomes. You can "trim down" your value lists by implementing a conditional value list where you first select a category and then you select a shift from a value list that lists only shifts from that category or you go ahead and set up an enhanced value list approach which can then definitely be set up with a pop up window like you describe here.