Alton, welcome to the forum!
I looked this up in J. Stills book, Weimar Lugers and it has Prussian police markings starting with either K. (kriminalpolizei), S.(Schutzpolizei), or L. (Landjagerei), the schools are listed as you were told, except for the first one is a bit different.
P.N. 439 There is a P.N. (it is in old script so bear with me), I think it is Police School Riederidlejien, listed as P.N., but nothing else exactly like it, and I could be seeing it wrong.
P. Fr. 439 The book does have PFr. as Police School Frankenstein, but there is not a period in the book until after the r.
If you re-barrel it, it will lose all collector value, depending on condition, a shooter is usually worth $450-$600, and if all original I would bet you would lose at least several hundred dollars in value.
Can you provide other information? Can you tell us any markings on the gun as numbers on the following pages?
Proofs? (see on your left under tech information if you came through
www.lugerforum.com) Tell us what and where proofs and markings are located.
There are forms in this section, where you can print out and then write down pertinent information.
What serial number is on the gun? To include any letters next to or under the serial number?
What year or letters are stamped on the top of the receiver?
What initials or letters are on the toggle?
Can you provide pictures, to include side, top, etc?
And of course it should, does not HAVE to, but should have a police safety and / or a magazine safety.
Ed