Script or workflow to modify find and replace text in clipboard
Try:

set myText to the clipboard as «class utf8»
set {TID, text item delimiters} to {text item delimiters, ":"}
set myText to text items of myText
set AppleScript's text item delimiters to "-"
set the clipboard to myText as text
set text item delimiters to TID
tell application "System Events" to keystroke "v" using command down