Hmm. The only way I can think of to edit a signature without messing with the code part is to go into the box with all the text, delete everything, and start over. Otherwise, the parts of the code you want to delete are things like If you delete those things specifically, the text should revert back to plain black text. Then you can change the info you need to change. Once the info is all in there, you can change the color and bold text by highlighting the text you want to change and clicking on the appropriate button.
I hope this helps you but if it doesn't, we'll work with you so you can get this done. :)