Need the ability to change the inventory costing method e.g. standard to average

I understand that you will have to reduce the inventory quantity to zero by "issuing out - negative adjustment" all the items to give you a zero balance and that is acceptable.

Once this is done allow the user to update the costing method of their choice.

Then receive back into inventory the quantity that was "issued out" using a positive adjustment.

As long as the user understands that the value being issued out is the same value being receipted back in and there is a record of the process and proof of before and after balances this process should be acceptable to auditors and to the business.