The install directory is the one that the Steam installer app has you use, but it does have to be changed. Windows 10 "protects" the Program Files directories, and doesn't like changes in them, like what a mod does. You'll have to de-activate all of your mods and un-install Silent Hunter: Wolves of the Pacific. Save your MODS folder for re-use later. Copy and Paste it into a temporary folder for safekeeping. If you use the advice from dodougla in THEBERBSTER's
SH4 <> TUTORIALS <> HOW TO DO IT <> INFO <> DOWNLOAD LINKS -STICKY INDEX, you log into your Steam account and do it there. When you re-install the program, create your own directory. A lot of folks will take the folder path and just delete the "\ Program Files (x86)" portion so that they then have "C:\ Ubisoft \ Silent Hunter..." Other folks will make a directory that they use for all of their games, such as "Games", such that they have "C:\ Games \ Silent Hunter..." That is your prerogative. Once you have the game installed in a different directory, Windows (for the most part) won't interfere with your modding efforts. However, let me point you at CapnScurvy's thread
Windows10; Large Address Aware; SH4 Install for installing the LAA app, and what else he does with his Windows 10 set-up to help. Don't forget to allow the DirectX9c install with SH4...