Excise duty can be treated in either of the ways as VA statements are non standardised. It is clearly stated in study material of financial reporting for ca- final provided by ICAI " Another contemporary criticism of VA statement is that such statements are non- standardised... Excise duty has been shown as part of bought-in cost and deducted while calculating value added. Some academics argued that such excise duty should be shown as an application of VA. However this practice of non- standardisation can be effectively eliminated by bringing out an accounting standard on value added. Therefore the criticism is a temporary phenomenon."
So, whichever method you will opt, it will be correct.
for your reference- https://resource.cdn.icai.org/19335sm_fr_finalnew_cp10.pdf > page 10.7 para 1.6