Hello Narendra,
What is that you changed in Model for Currency & Date ? ABAP Types or EDM types ?
I don't see any conversion needed until you face any dump while mapping back the response to GW.
Normally GW frame itself will pick the appropriate data types based on the data types of the abap fields.
Are you getting any error when you consume service ? What is that made you to think some conversion is needed for the data fetched from Table before mapping it to GW response structures ?
Regards,
Ashwin