My understanding is you can use any Series operations without penalty (ie. they get passed into some rust NIF call), https://hexdocs.pm/explorer/Explorer.Series.html#functions-s..., which does include whitespace trimming, but not arbitrary strings, but I imagine it wouldn't be too much of a jump to add arbitrary constant strings. Might just need to expose `str.slice` or `str.replace`.

The docs do imply that `mutate_with` operates lazily, so you only pay the transfer cost once per row, no matter how many mutations you're applying, but whether that's performant enough depends would be case by case.