I am inclined to agree with KaleunMarco, jldjs... There are a couple of options though. First, copy and safeguard your Save folder, like if you have it named FRS or whatever in MultiSH4, then copy it and move it to a different folder, but name it something memorable, so you do NOT lose it for this crazy experiment... You could either try what you suggest then with the other, copied file-set as a "safe-guard" (remember though, it does probably have "corrupt" data in it...), but you will most likely either crash while loading, or while entering the sub. If you try that first and it fails, delete from "data" on down in your current Save folder, and bring back in the "safe-guarded" copy from "data" on down.
Come on in to port, and dock. Accept your new boat. Once back in the office, save and exit. Do NOT look at your new boat, do not go on patrol, etc. Now apply the patch. Start the game again and look at your new boat. Does it have a gun? If it does, fantastic. If not, look at your system clock and note the time, and make a new Save, different name of course, and exit the game. Go into the Saved game files and find the timestamp for the latest save folder, then use either the "ColetrainsAndOthersDGfix.pdf" file, as found in the Support folder of the FotRSU mod, or KaleunMarco's package, as previously linked. See if you can get gun positions back that way. If not, it is probably hosed... sorry. You could attempt to go on a short "training" patrol that goes outside the "home port" area (go beyond the green circle and for at least 24 hours) and see what happens when you dock the 2nd time and then come back into the game.
A third option would be to copy that "safe-guarded" Save data back in to the Save folder, and come into port and dock. Refuse the new boat. Once in the Captain's Office, exit the game and apply the officer country patch. Now re-start and do some more patrols, and accept the new boat the next time you are asked, and see what happens then. Be sure you are saving each time you come in, and to a new name each time...
Let us know though, how it goes for you!
