Welcome to Subsim Redwake. There should be no reason why you shouldn't be able to modify the stock version of SH4. You can read about SH4 on the Subsim forums.
http://www.subsim.com/sh4/silent_hunter4_addon.php
The U boat add on is also available for a nominal fee. Amazon has it for 10.00 dollars.
https://www.amazon.com/Silent-Hunter.../dp/B004I43FAG
The Silent Hunter 4 Gold edition which has the U boat add on is available for $ 20.00
http://www.gamersgate.com/DD-SH4GE/s...4-gold-edition
https://www.amazon.com/s/ref=nb_sb_s...d=HMXIX4WHHK0W
Further, UBI Soft support, which created the Silent Hunter series has a patch available for SH4 as well. Further, UBI Software should have all the patches you need , free to download.
( This is the link for 1.2 patch for SH4 )
http://patches.ubi.com/silent_hunter...nter_4_1.2.exe
( This is the UBI Software link for the 1.4 patch )
http://patches.ubi.com/silent_hunter...nter_4_1.4.exe
( This is the site ) Look through UBI software for any up to date patches you require.
https://support.ubi.com/en-GB/Faqs/D...-does-this-fix
I hope this helps. Enjoy your simulations and welcome aboard.
