I've recently helped the DO I've been shadowing draft my personal statement.
Personal statement? Don't you mean LOR?
Please feel free to correct me if I don't get the story right, your DO like your version of the LOR and want to keep it for future uses, but you prefer him not do that, correct? Well I presume your draft must be a masterpiece then.
IMO, if this is really a big deal to you,
wait until he submits the letter then:
1) Politely ask him not to use your letter as future reference.
2) Softly tell him to edit the letter for future students.
3) If you're accepted, then who cares at that point?
However, I wouldn't like it if any of my mentor didn't write me a strong letter. I didn't read any of my LORs, but was told that all of them were uniquely written for me in a way that they could not be replicated for another student.