In the absence of a sample table, your requirement doesn't appear to make sense.
What the code appears to suggest is that if the row height is 6 point (which seems improbable) then the row is formatted as with your first set of codes, whereas if it is greater than 6 point (which seems to be the more likely scenario) it is formatted with the second set.
The only difference between the two is that the second set has the text aligned to center, whereas in the first it is left aligned.
Code:
Sub FormatTables()
Dim oTable As Table
Dim oRow As Row
For Each oTable In ActiveDocument.Tables
For Each oRow In oTable.Rows
With oRow.Range
.Font.Name = "Arial"
.Font.ColorIndex = wdBlack
.Font.Size = 11
.Cells.VerticalAlignment = wdCellAlignVerticalTop
.HighlightColorIndex = wdYellow
End With
If oRow.Height <= 6 Then
oRow.Range.ParagraphFormat.Alignment = wdAlignParagraphLeft
Else
oRow.Range.ParagraphFormat.Alignment = wdAlignParagraphCenter
End If
Next oRow
Next oTable
lbl_Exit:
Set oRow = Nothing
Set oTable = Nothing
Exit Sub
End Sub