Yes, Unload-Reload can be used to compress the record. The new subschema specified in the unload and reload jobs would specify the new subschema with the compression defined.
If using the IDMSCOMP/IDMSDCOM compression calls remember:
If any record in the area uses IDMSCOMP and IDMSDCOM for compression and decompression, the area should have the following database procedure specifications:
call idmscomp before finish
call idmsdcom before finish
This ensures that the work areas used by the compression and decompression routines are freed when a rununit terminates.