You need to add users to a user group on tableau.

or Active Directory Group if you are using AD

then the user filter should be amended to user group filter.

This way you don't need to keep downloading and republishing each time you need to add or remove a person.

You either need to add them to user group on server or add them to AD group on network.

You will have to create individual groups for each sales area

which might be too big of a task depending on number of areas.

The other thing you can do is build in another datasource with manager names and their sales areas.

then user filter formula should basically check which user it is and filter to show only their sales area.

In other organisations I've had difficulty getting hold of a username table with up to date position and location

due to HR holding this information and all the red tape in a large organisation