You can have the image of your source file given to him in that format they want rendered unusable for changes.
You convert even the text to objects then ungroup. The school district union employee wanting to mass template your work could see it, high resolution print it from that file but would be screwed trying to change it and could not use it as a template.
I did that myself before.
Took seconds to change it. Not much extra work for you.
I don’t think you can change a PDF. That is the only form of the document I gave him, so that it could not be changed.