Assuming the schema where you will store the stats to be imported is called "TEMP_STATS_SCHEMA" and you have a source schema called "SOURCE_SCHEMA" and a target schema called "TARGET_SCHEMA", the command syntax is as follows:
exec dbms_stats.create_stat_table(ownname => 'TEMP_STATS_SCHEMA', stattab => 'TEMP_STATS_TABLE');
exec dbms_stats.export_schema_stats(statown=> 'TEMP_STATS_SCHEMA', stattab => 'TEMP_STATS_TABLE', ownname => 'SOURCE_SCHEMA');
update TEMP_STATS_SCHEMA.TEMP_STATS_TABLE set c5 = 'TARGET_SCHEMA' where c5 = 'SOURCE_SCHEMA';
commit;
exec dbms_stats.import_schema_stats(statown=> 'TEMP_STATS_SCHEMA', stattab => 'TEMP_STATS_TABLE', ownname => 'TARGET_SCHEMA');