While I agree this would be a great built-in option, you can build your
own.

I use this macro

Public Sub CenterAcrossSelection()
On Error Resume Next
Selection.HorizontalAlignment = xlCenterAcrossSelection
On Error GoTo 0
End Sub

attached to a button on my custom toolbar.

In article ,
Plantimacros wrote:

As a selection of a range of cells, and the copy and paste action are afected
when crossing a merged cell, I prefer to center cells across selection, not
to merge them; it will be usefull to have a bar button with this command.