Can you test recording and reversing a new fixed asset acquisition posting in your demo environment with the parameter activated?
It might be the case that activating the parameter retrospectively does not allow reversing the old voucher.
Another possibility is that the voucher is too complex and comprises transactions in the GL, AP, tax, inventory ... modules. If this is the case then AX cannot reverse the voucher automatically even if the parameter is active. Your only chance is then a manual correction posting.
Best regards,
Ludwig