Extend range of existing conditional formatting to further cells?

I don't think you can edit the Conditional Formatting. I suspect that you have to delete what's there and re-apply it.

This is a recorded macro to set up CF in cell C7 to C19

Sub Macro2()
'
' Macro2 Macro
'

'
    Range("C7:C19").Select
    Selection.FormatConditions.Add Type:=xlExpression, Formula1:="=C1="""""
    Selection.FormatConditions(Selection.FormatConditions.Count).SetFirstPriority
    With Selection.FormatConditions(1).Interior
        .PatternColorIndex = xlAutomatic
        .Color = 65535
        .TintAndShade = 0
    End With
    Selection.FormatConditions(1).StopIfTrue = False
End Sub

And this is a macro which will loop through all the CF on a worksheet and create a list of the ranges and the formulas

Option Explicit

Sub lsform()
Dim cf As FormatCondition
Dim rng As Range

Dim vArray, i As Long

Set rng = Cells

If rng.FormatConditions.Count = 0 Then
    MsgBox "No CF"
    Exit Sub
End If

ReDim vArray(1 To rng.FormatConditions.Count, 1 To 2)
i = 0
For Each cf In rng.FormatConditions
    'Debug.Print cf.Formula1, cf.AppliesTo.Address
    i = i + 1
    'build array of conditions and addresses
    vArray(i, 1) = cf.Formula1
    vArray(i, 2) = cf.AppliesTo.Address
Next cf

' output array to same sheet, specified start cell
With Range("G1").Resize(UBound(vArray, 1), 2)
    .NumberFormat = "@"
    .Value = vArray
End With
' output array to another sheet, specified start cell
With Sheet2.Range("A1").Resize(UBound(vArray, 1), 2)
    .NumberFormat = "@"
    .Value = vArray
End With

End Sub

You can also check the interior color and the font color, etc:

?cf.Interior.Color
 65535 
?cf.Font.Color
Null

So, if you first establish the range, the formula, the background, font, borders, whatever, you should be able to adjust the range and re-apply the CF.

You're welcome. Thanks for the rep.