You can do his but only with vba code.
Is the current word art one of the preset styles from the ribbon and do you know which one??
Here is sample code to swap the first preset to the fifth - adapt to suit the presets you need.
Sub WA_swap()
Dim osld As Slide
Dim oshp As Shape
For Each osld In ActivePresentation.Slides
For Each oshp In osld.Shapes
If oshp.HasTextFrame Then
If oshp.TextFrame.HasText Then
If oshp.TextEffect.PresetTextEffect = msoTextEffect1 Then _
oshp.TextEffect.PresetTextEffect = msoTextEffect5
End If
End If
Next oshp
Next osld
End Sub
How to use code