Hi Nishant,
I suppose you're trying to use WP_EAN to generate the GTIN specific message in WPMA.
This is, however, not really feasible in standard (the same for WP_PLU). The logic behind downloading EAN references simply takes the selection criteria, determines corresponding article and sends out all GTINs defined for the POS UoM as maintained in the article master.
You cannot use the EAN select-option to restrict the GTINs downloaded and I am afraid it's not really possible even in the relevant user-exit EXIT_SAPLWPDA_003 as you might not have the visibility of the selection criteria (ask an ABAPer though) in RWDPOSAN (WPMA).
I see it as a change request with custom development reusing probably function module MASTERIDOC_CREATE_DLPEAN to generate the message and then modify the IDoc accordingly by applying the restrictions specified in select-options of the main program.
Sorry for the rather negative message but I hope it helps anyway!
Cheers,
Tomas