Panda, this is an AMAZING discovery.
I tried this myself, and me being a Lucas main, this has proved very useful.
I also did some other experimenting with the button configuration and i found something that MAY prove to be useful.
I tried replacing B with jump, kept A as attack, Z as another attack, both X and Y to jump, L to grab, R to shield, with tap jump on.
As a result:
I can do the b-stick PK fire with ease by using the B-stick and tap jump.(can control direction of B-stick PKF by jumping in a diagonal jump)
I can still grab With L
But most importantly i found something else out with B being another jump button. You can do a shorthop aerial (with the exception of up-air) just by sliding your finger from B to A as quick as you can.
The point here is not even close to how convenient it might be, its just that you can press a button in the fashion of a full hop and still be able to shorthop-aerial. I just find this an interesting topic because when i try to do things fast, i more than often end up pressing a button too hard or too lightly.