Are you referring to adding a link using weblair? I just tried adding links to local and remote pages with the ! character and it placed them without an issue.
Can you elaborate what the issue is?
Did you try changing the Tools-Customize-Spelling, Valid word characters to
When I did this the whole name was underlined and I was able to right click and select Open to open the link in my browser. I then removed the ! and ME went back to the behavior where the underline stops before the ! character. Like I said the change requires a restart.