I cannot determine what your actual question is here, but I will try to give you information that may help, based on your statements.

You cannot modify tax settings in QIP if open invoice batch(es) exist. You must either post the batches, or you can archive them, make the necessary changes to the tax tables and tax types and then restore the batches into the invoice batch area afterwards.

You can then (if necessary) use the Block item adjustment option (in Housekeeping - Item maintenance) to change specific items (or a range of items) tax type from what it used to be to a new type. Also, if necessary you can use the Maintain Archive batches - Update archive system to update tax on invoices in the archive area.

If this is not the problem - please steer me in the right direction with a more specific question.

Regards