FM/BAPI to update resource allocation to an PS project activity

Hello All,

I am allocating an resource to an activity of a project through transaction CM27. Now based on the value of the Activity I need to to allocate the same resource to some other activity of the same project. I am trying that with FM 'CY_BT_KBED_OPR_UPDATE'. but I am not able to update 2nd actvity. Can some one help me on doing this with this function module or some other?