Hi Mario,
as far as I know it is not possible with standard settings in the system copy tools.
Technically it might be possible when executing R3LOAD manually (see SAP note 2148354), but this will be by no way supported by SAP. Please note that as of NW 7.5 based systems, Unicode is the only option (see SAP note 1322715 - topic 6).
This raises the question why do you want to do a conversion from Non-Unicode to Unicode ?
Best regards,
Nils Buerckel