Yes, you can let your hairdresser dye the human hair products darker. However, we do not recommend bleaching or lightening human hair products, as this would severely damage the hair. White, Platinum Blonde, and light grey hair are the best colors to use if you want to dye to a darker color. If you want to risk taking the chance of lightening with bleach, then we would suggest to test strand in an inconspicuous spot first.
Synthetic hair products cannot be dyed with regular hair dye. We strongly do not recommend you dye a synthetic hair product since it may cause irreparable damage.