I managed to get a half asses solution going.
Using a hotkey I trigger a terminal command that consists of the following python script:
#!/usr/bin/env python3
import re, pyperclip
text = pyperclip.paste()
result = re.sub("(^\\w+)(:\\s)([^\\0]+$)", r"\1 - \3", text)
pyperclip.copy(result)
This modifies the clipboard and readies it for pasting. Unfortunately it also opens up a terminal window.
I wish I knew a way that this could all be done in the background without all the extra work, including the final paste.