Going to WC3 in the Battle.net launcher, go to launch editor.
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In the map editor go to the campaign editor
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Now go to File -> Open Campaign -> (Updated) CSW
Wait for it to load it's not actually stuck.
Go to the Loading Screen section, you will see the various chapters.
Double Click the mission(s) in question that you want to have unlocked -> Click visible on Visible don't mess with cinematic.
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Do this for every mission you want to have unlocked or have already done. Now go to File and then Save Campaign.
As long as you edited the campaign file you have in the campaign folder you don't have to do anything else otherwise you'll need to remember to put the edited campaign file into the campaign folder, and as long as there is no problems with your cache you can continue from the latest mission you were on and your heroes should have all their items.