Assuming that it's not changing perspective or moving around too much, I would use a tracker on the tattoo and a clone stamp from another area of skin. More elaborate removal could be done with Mocha, or using a mesh warping tracker like Lockdown, which has a demo of tattoo removal in their showreel at 0m24s:
You have control over this. If you use the correct settings, you will work on the original file.
When you setup a project you can define what Ingest Settings to use during import. Those settings can also be changed later. In your case you probably want to use Copy.
If you drag and drop a video from the Media Browser panel to the Project panel the video will ...
I have used Real-time Voice Cloning for this purpose. The quality isn't great, but it works for US accented voices better than UK in my experience (Gandalf = Ian McKellen = English). Maybe this would be better in Sound Design?