Matthew,
You can do this by creating an associated entity with the changing list of values. The drop down would be a reference selector, which can be populated in a number of ways, including by microflow.
Here is an example:
Domain model showing Orders entity. Each Company can have many orders:
On an Order_NewEdit page, you can then have a Reference Selector to choose the company for the order:
In the reference selector, you will find a list of Companies. The documentation provides details on how to configure a reference selector.
Hope that helps,
Mike