Chris,
What you have described in fin marking/drain holes is some what old hat dating to the 1950-60s from the very demanding and prestigious Los Angeles County UW Instructor association programs. As you probably know since you live in LA Co, this was the first origanized diving instructional program. Founded in 1954 it is the father of all other major instructional programs; NAUI in 1960 and PADI about ten years later.
The participants of this three month long very intensive program were divided into "dive teams" of about 4 to 6 divers under the leadership of a "Dive master*." (*the origin of the name "Dive Master" ) Each team had a color, to denote their membership; ie red, blue green and of course Orange for those living in Orange County, AKA "The OC."
During the course the BOTTOM of the candidates and the Divemasters (Instructors) fins were painted the appropriate color of the team membership. This was to insure underwater visability and that any strays swimming away from the dive training event area could be immediately recognized and directed to their respective team.
The paint used was a cheap spray paint which could be left on after the completion of the course or removed with paint remover.
During the three months of the instructor training there was approximately 100+ immersions in fresh and salt water. I do not recall a fin ever being repainted. However do to enviromental concerns paint formulas have under gone considerable changes since that era and modern paint may possibly react differenly to rubber and repeated flexing.
The drain holes in the fins of that era were made as mold release holes during manufactuing process. Some were open and some were closed even from the same manfacture but possibly a different lot. Some of the instructors liked them closed others open, some even made additional drain holes.
The drain holes were opened, often enlarged or new ones made with the end of a wire coat hanger heated over a gas or electric stove until glowing red hot. The coat hanger was grasped with a pair of pliers and the hot end of the coat hanger was thrust into and through the fin, making a new hole or enlarging an old one, concurrently vulcanizing the the hole to insure that it would not further rip or tear. I do not know if it would work on the new modern fins or if the heat would create a toxic enviroment, so K MAG YO YO.. However I would suggest that you experiment with the coat hanger method as well as the use of a drilled hole as proposed
An added discovery was the that coat hangers could be twisted and bent in to various shapes creating initials, symbols etc. Once again when heated and applied to the back side of the fin tip, the fin was branded forever just like the cowboys did their cattle in the old and modern western US to denote ownership.
So that is the way it was done in the genesis, beginning of recreational diving instruction, almost fifty years ago. Thanks Chris and all for kicking off long dormant memories and allowing me to bore you. Now I will awaite your learned comments...
Chris, I seldom monitor this board but appreciate to hearing from you as to the method you used and the results obtained.
SDM