Lets say my body reverted back to the to match my mental maturity level and I became a kid again. During school when everyone stands up to say the pledge of allegiance I proudly declare "I pledge allegiance to the flag .... One nation under Satan Indivisible ... etc"
I suspect some of my teachers may not approve of my modification of the pledge, but would the school be able to penalize me for my variation of the standard pledge if I argue it's in keeping with my religious beliefs?
We know the school cannot compel me to say the pledge of allegiance, but in this example I would be willingly saying a variant of the pledge. On the other hand I probably couldn't stand up during the pledge of allegiance and start shouting random gibberish since that would be disruptive behavior which schools are free to prevent. My pledging to Satan would likely also be construed as potentially disruptive behavior, but I would presume that would not outweigh the protection of speech/religion afforded by the 1st amendment?
If I wouldn't get protection of religion on the grounds that a belief in Satan isn't a 'firmly held belief' of mine you could always replace Satan in this example with Allah, Jehovah, Shiva, Odin, Flying Spaghetti Monster etc.