A 1944 pattern Lincoln penny that went from MS60BN to MS65BN after I delicately conserved it with innocuous compounds. That removed gunk had really subdued the electrifying silvery cartwheel luster. CAC even approved it in its MS65BN slab!
But I know one dealer who could sometimes turn BN copper into PCGS RD! But he also ruined many as I did. Copper conservation is always a crapshoot. Definitely not for the faint at heart. You never know what is under the gunk.
I have always had the best results with BN copper. If it has too much RD, conservation will likely ruin it.
FYI, many of that dealer's BN to RD coins turned in their slabs within mere months. Poor PCGS probably had to eat them.