I don't think so. I believe the easiest way to accomplish this, is that when the shell is in motion, I'd simply cycle a few CHR pages into the VROM slot that has the shell graphics in it. I'll look into it.
But first, I don't know if anybody has noticed this, but there is a major bug in the game that I overlooked, that needs to get fixed in order for the game to be fully playable.
When you reach Mouser at the end of World 1, if you try to catch the bombs, or walk into them after they have fallen on the floor, they can hurt/kill you. And this goes for the bombs that you get from the vegetables as well.
I believe this bug occurred when I made the turtle shell hurt the player. Originally, the turtle shell would simply pass through the player, so there was a certain kind of passivity to it. I believe this same passivity applied to the bombs as well. The only time the bombs hurt you is when they explode. I have to go in there and fix that.
Also, I noticed that in subspace, if you jump up to get the mushroom from below, you won't be able to get it. I have to fix that as well.
So, Version 1.2 will be coming soon. I'm not sure when, as I have to study this weekend for my final exam on Monday. But it will come soon.