It's not possible to change certain transitions in the way you describe. The reason is "Wedding Day" is not text, it is an object that looks like text.
I hope that makes sense to you. It would be the same as asking if you can turn an elephant into a zebra.
What you can do is remove that object and replace it with your own real text. If you want to keep everything the same as far as motion, color scheme, etc then it would be a good idea to save a copy of the envelope for "Wedding Day" as well as the other parameters and use it on the new text you create.
Joe
PS I am looking in folder 18-Weddings and the file is called BAS-Wedding Text. Even though it says text, it's not text. If you have XP, look in C:\Program Files\PInnacle\Hollywood FX for Studio\6.0\Objects\18 - Weddings and you will find Wedday Text.hfo