"Impossible"? No... likely more difficult (especially considering the type) yes, but certainly not impossible.
Well, all ancient coins come out of the ground looking like this...or worse! Most are actually so heavily encrusted you can't even tell what type of coin it is at all. So when you buy it like this one below, you can be sure it's been cleaned and will always be a cleaned coin. So cleaning is the norm with ancients. So since you have a cleaned coin, any cleaning is ok, as long as it's gentle and well done.
I bought a Morgan some years ago in an off-slab with a crazy MS-69. Coin appeared to free of any derogatories, and looked like a 65 with an outside shot at 66. I paid low UNC money for it, then Sent it to California..came back 65. Was worth it, as catching the 5, as with many Morgans, means a significant jump in value. And then there was the coin I did not crack, after speaking to legendary John Albanese. EBay purchase of 1891-CC in PCGS 64+ with green bean. Check your sheets to see huge jump between 4 and 5 for this coin. I was familiar with the bean, but wanted to go to the source. Did not expect JA to answer phone...but...found him to be most gracious and willing to edumacate me. Can't recall exactly what he said, but it was clear he did not think cracking was a good idea.