Did you even read his post? He's not looking for YI grassland ExGFX, he wants to have layer 3 flowers in front of them.
Anyway... Yeah, that's possible, though it requires a bit of ASM knowledge. You'll have to make the flower graphics (you'll probably want to use the Layer 3 ExGFX patch, since you'll overwrite many other layer 3 tiles for all levels otherwise), and turn them into an image using the Stripe Image patch. A much easier way, of course, is to simply use layer 2 for the flowers and give them layer priority. That will mean you can't use a background in that level though.
For your second question... Yes, you'll need to edit the springboard's GFX. (I think I remember seeing a custom sprite of it somewhere, but I might as well be wrong.)