SH5.exe will be changed after the generic patcher, a way to know if things have been patched correctly, and other 4 files also patched. And AFAIK, no, it's not only recommended it's necessary, only that other mods don't tell about and you see a lot of posts about SH5 not working here in the forums. Also it's the only serious reason why Steam versions don't work: It cannot be patched, end of the story.
Quote from TWoS thread:
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Step 3:
Properly activate TDW Generic Patcher and restore "
TWoS 2.0_Snapshot.gps". The patcher, snapshot and install instructions are already placed in the main game folder (
Silent Hunter 5/TDW_GenericPatcher_v_1_0_168_0).
How to properly activate TDW Generic Patcher.
(Steam version doesn't support generic patcher and therefore this expansion too) Advanced workaround for Steam users
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Forget about the 'Advanced workaround for Steam users', instead get a non-Steam game version. Or please Subsim.com make these famous 5 patched files ready for download...This would also allow us to bypass the hilarious step 3 above (and make Steam users happy).
Alas I understand that this is not possible without permission of Ubisoft or its relegate licensees. The losers are the Steam buyers.
To know if TWoS or your mods work correctly, start a single mission, fire your torpedos. If they circle around you know the game is not setup correctly. Then, if you can go past several campaign chapters without trouble then your SH5 game works ok. Most of the starting players don't go until there and think they are fine, but it ain't so, not with the Steam versions, and not with any UPlay crap... I haven't seen...
***> 1 <***
... serious post in Steam that the game works. For those saying the contrary, I just don't believe they have played very far in the game...
But I'll stop from now giving advices, they go in the void. I have already answered OP in the Steam forum, so he is warned.