If you have a complex document to edit, it may be easier to use a specialised HTML editor to create the page - that way you will have more editing options available.

How can I edit a hyperlink that I've created in a message that I'm composing or editing?
Thanks,

Do you mean one that you've put in with the 'chain' icon?

I think you have to delete the old one and replace it. 

It would be great to be able to edit hyperlinks in a message being composed or one that has been saved.  I have some messages that have 30 or more hyperlinks.  Also, I tried to "export to a text file," but all I got were the message headers.  I thought maybe it would show me the hyperlinks.