I had one similar moding experience with one my 5 years hold DRSD non MBW.
I always used on swimming pool and diving on all the see around the world.
Two mouths ago I get a lot of mods (just to get my experience):
holes fro gen springbars , GEN Crown and tube , gen Tropic , case reshape etc.
During the mods I broke the original glass, so I tested to fit one T19 ( the T39 was too high for that light non correct bezel).
Here some pictures:
To get the T19 tropic, the problem was that the Gen tropic was bigger than the case seat.
So I had to glue it with epoxy, and to be safe of the work done, I get one waterproof testing.
The DRSD passed 2 ATM test without problem.
I used it on my 2007 holidays diving at the sea and swimming without problems.
Now I get one MBW and I'm modding it