Hi Prateek,
'data does not get saved' is not clear enough. Maybe the 'comment' simply is not input-ready. You should use proper formatting in the EPM Add-In or use AO or RSRT to check whether the cell you try to change is really input-ready.
You can have the amount in an InfoCube and the 'comment' in a DSO, this is no problem at all. But you have to ensure that the cell coming from the DSO is input-ready. Most probably some restrictions are missing, e.g. the currency. As I said, to write data back to a DSO all key fields have to be uniquely determined (including 0INFOPROV, unit, currency if used); you may use disaggregation then you can change also aggregated cell values, in case of key figures with aggregation NO2 then disaggregation 'copy' is used. But the characteristics 0INFOPROV, unit, currency if used always have to be uniquely determined.
Regards,
Gregor