Yes it can be done, I have some major scarring which I am currently getting covered.
As a rule, the older and flatter and paler the scars are, the easier they are to cover, and the better they 'take' and retain the ink.
Red, raised and fresh scars are harder to cover, I have been putting BIO-OIL on mine, its a little expensive but it works miracles.
You really need to discuss it with your tattoo artist, good luck

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Regards.
Vin