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The patch provided doesn't take into account the very unusual action of changing the entire store from tax-added to tax-included. That requires manual editing of each price to remove the tax...

Exactly. That's why we encourage people to "do it right the first time", and find long-term fixes instead of using tools dangerously without the knowledge required to be safe.

Then your active tax class isn't number "1". Change the "1" to whatever your active/desired tax class is.

Or just change every product manually.