I've been struggling to make up my mind about this. There is no simple answer to how to deal with this question where old songs (or indeed any old works of art) are concerned.

What aspect of it might be unacceptable? Even when "Moor" was used to describe black people I'm not sure it was necessarily a racial slur, simply the usual term, much as "black" is today. In modern usage the term "Moor" is used only in the context of the mediaeval Muslim occupation of Spain. The term is widely used and is not considered offensive. Whilst the sense of the lyrics are clear, no one today would describe a black person as a "Moor", even if they come from the Maghreb. There should not be a problem with the word itself.

The song refers to the sooty appearance of the sweep which makes him look like a black person. Is this offensive? I sense that it might be, but I'm not entirely sure why. The comparison is purely factual and descriptive and is not derogatory. However logic does not always apply to these situations, and I can see that some might be uncomfortable with it.

There is a suggestion in the lyrics that despite looking like a black person the sweep is in fact a jolly good fellow, so this might hint at underlying racist attitudes which are no longer acceptable. In that case, alternative suggestions such as "black as any crow" don't alleviate this. However to excise these verses is to remove much of the song.

I can see a justification for content warnings on TV programmes where viewers are mainly passive consumers who may start to watch a programme with little prior information about what they might see. I would expect a folk club audience to be aware that these are old songs and of their time and most do not reflect modern ways of thinking about many things, and I do not routinely feel it is necessary to explain this. However that might depend on the audience.

My personal conclusion is that whilst this song might make some listeners uncomfortable it is not egregiously offensive. It's not in my repertoire but if it were I would not change it. I can also see that others might take the opposite view and I respect that. As I said at the beginning, there is no simple answer.