Changing graphics of Samus and her shots

[Shidomaru]

Greetings! These are going to be my first questions, but certainly not my last.

I'm using SMBX 2.0 Beta 3 to make a game with "Samus" as the player character... Except I'm changing the graphics! Now, I've ran into two problems with this:

1) The character graphics I'm using are vertically shorter than Samus, meaning I need to change Samus's hitbox size (the character is not meant to float), BUT I also want the hotspot where her shots spawn to change accordingly, so that my character doesn't end up firing from his forehead.

2) I'm having difficulties changing the graphics of Samus's shots. Just placing the "samus_shot.png" file in the episode's root folder does nothing! Same goes for "samus_missile.png"

So... Any ideas about how I can handle this?