Hi Anwesha,
Hope 'result_package' that you are using in loop is an internal table that contains data of Transparent table 'result_package'. May be the values that u r assigning to structure wa_result_package is not reflecting as you have used same structure in loop. Try this:
loop at result_package into wa_result_package.
read table it_sal_off into wa_sal_off with key sales_off = wa_result_package-sales_off.
clear wa_result_package.
if sy-subrc = 0.
wa_result_package-sales_off = wa_sal_off-sales_off.
wa_result_package-country = wa_sal_off-country.
modify result_package(transparent table) from wa_result_package.
endif.
endloop.