Hi Anindya,
If you are at HANA SP6 you can write back the data to HANA using XS.
As explained by Sakthi you cannot write back the data to BW directly using XS,write to HANA use it in any views and then consume that view in BW via virtual cube or transient provider.
If you are in BW7.40 then via ODATA service you can write the data back to BW.
Hope this answers your query.
Thanks & Regards
A.Dinesh