Hi Elle W
To edit field aliases on the data source in Pro, open the Fields View. That can be done from the layer's context menu > Design > Fields
Or from the Attribute Table triple-stack menu > Fields View
Or from the Table View ribbon... anyway, you get the point; there are different ways to get there.
From Fields View make sure that you change the dropdown at the top from the Layer name to Data Source
Now changing your aliases can be done directly on the data source so that it is permanent.
Does that help?