It is best to use COD, ...
Published by Jeremy Biddle, Engineering Director at Bluewater Bio
It is best to use COD, rather than BOD, as the primary metric for the plant load. COD is a conserved parameter (i.e. you can do a mass balance on COD through the plant) whereas BOD is just a measure of what is oxidised by the inoculum in 5 days. Nearly all of the COD will be removed in your treatment plant, either by oxidation or assimilation, so the COD will give a better estimate of the oxygen demand.
As has been said by others, peroxide might increase the BOD by converting slowly-degradable organics into measurable BOD, whereas peroxide will cause a reduction in COD.
You haven't specified what problem you're having with a high BOD. Is it just that you are having problems measuring BOD accurately or is your plant overloaded (high COD load)?