is this (ab)use of -p blessed by p5p and/or Larry?

I can't speak for them of course, but I would venture that it's allowed with the understanding that the -p "template" could change in the future in subtle ways that would break this type of "use".

On the other hand, given the use of source filters such as Perligata and Lingua::tlhInganHol::yIghun (Klingon) (which unfortunately I can't find the actual module for), it seems that the Perl community would have an interest in making the language stable under these uses. [I'm sure I've made some gross error concerning source filters, but I'll just encourage the community to correct it here, and enlighten the rest of us.]

Considering the simplicity and elegance of the template approach for -p and the like, I feel comfortable that that abuse is stable as well.