Actually, you can enable/disable dual wielding on the weapon rotation keys with
Sandbox+.
R + Down ... enable/disable dual wielding on weapon cycle
R + Home ... cycle pistols
R + PageUp .. cycle smgs
This is also useful if you want to downgrade weapons.
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There is also a
save editor that can remove the upgrade
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Here, it works the same way as
JoeyBeanz's mod, so give that a review if you find any trouble. If you want to remove any more upgrades, just delete them from the table file using a program like
notepad++.
Edit: Install into... C:\Program Files (x86)\Steam\steamapps\common\Saints Row the Third
Edit:
Warning: Dual Wield cannot be repurchased after mod is used, backup your save beforehand.
Edit: Updated files, now includes removal of all weapon upgrades.