Change visa from single to double entry?

Hi, I am a Canadian living in Dubai. I was granted a visa to China for single entry, and I plan on going to Shanghai, then Hong Kong during my stay and, then return to Shanghai before coming back to UAE. I didn't know that going to Hong Kong is considered an exit. I still didn't travel to China. Can I go to the consulate before travelling to China and ask them to change my visa to double entry instead of single? Can you tell me if there are any additional requirements if this is possible please?