How to Create Dynamic Default Slicer Value?

I actually was able to crack this problem!  I will attempt to break down how I achieved this.

I created a Slicer Table with:

Slicer Table = 
UNION(
    SELECTCOLUMNS(
        'ORION - Posts',
        "PostName", 'ORION - Posts'[PostName]
    ),
    DATATABLE(
        "PostName", STRING,
        {{"Current Post"}}
    )
)

Then I have a user table with the locations tied to their principal user names by email and use this measure to lookup the post name:

UserPostName = 
LOOKUPVALUE(
    'UserLocationData'[PostName],
    'UserLocationData'[email], USERPRINCIPALNAME()
)

Back in the Slicer Table, I created another measure to use the user's post name if "Current Post" is selected in the slicer.

SelectedPostName = 
IF(
    SELECTEDVALUE('Slicer Table'[PostName]) = "Current Post",
    [UserPostName],
    SELECTEDVALUE('Slicer Table'[PostName])
)

The biggest issue I was having was that other measures would not calculate correctly.  This is solved by adding a variable into each measure.

LES Count = 
VAR SelectedPost = 
    IF(
        SELECTEDVALUE('Slicer Table'[PostName]) = "Current Post",
        [UserPostName],
        SELECTEDVALUE('Slicer Table'[PostName])
    )

VAR EmpCount = 
    CALCULATE(
        SUM('DAFI - Personnel Data'[count]),
        'DAFI - Personnel Data'[employeeType] = "Locally Employed Staff (LE Staff)",
        'DAFI - Personnel Data'[site] = SelectedPost
    )
    
RETURN
IF(ISBLANK(EmpCount), 0, EmpCount)

However, I had to deactivate the relationships for:

• 'Slicer Table'[PostName] to 'ORION - Posts'[PostName]
• 'UserLocationData'[PostName] to 'ORION - Posts'[PostName]