I can't believe you (you!) typed that.
Agreed. The subtext is “Everything is prohibited, unless we have given permission.” Many conservatives have deep recesses of their minds that the left has colonized.
I guess it depends on how prevalent horses are where you live. I wouldn’t dream of letting my kids ride a horse in the parking lot dressed up as a character without having it cleared with the school officials first, unless it was a day when everybody was told to do something related to school spirit that was wacky.
Generally, I tell my kids that if they are planning to do something where, if everybody did it, there would be havoc, they should probably ask permission first.
If the school knew what the kid wanted to do, maybe they would arrange for it to be part of a pep rally, a more controlled circumstance.
But like I said, it could be different if you are in an area where horses are more normally found out in public.