August update brings a new 'Find and replace cells in Excel worksheet' action, but it doesn't work in a specific range of cells.
Try this:
1. 'Launch Excel' with you file
2. 'Focus windows', window class = XLMAIN
3. 'Select cells in Excel worksheet' and select your column headers
4. 'Send keys' {LControlKey}({U}) 'Ctrl + u: replace shortcut
5. 'Send keys' {Space}{Tab}{LShiftKey}(_)
6. 'Send keys' {LMenu}({T}) 'Alt+T
7. 'Send keys' {Return} 'Enter