I would personally choose to add an introduction and republish unchanged, but EB is often repellently classist, sexist and racist.
One which I know has had alterations made in a reissue is The Island of Adventure, which reads quite weirdly if you don’t know it’s been altered. Originally the villain is the black servant Jo-Jo, who is a caricature — violent, threatening, strong, but also shiftless, lazy, cowardly, ignorant and superstitious, bossed around like a child by his employer, his race referenced all the time, speaking a kind of patois possibly intended to be Caribbean, always ‘rolling his eyes’ so the white show when afraid.
(In the reissue, he’s Jo, no race mentioned, and ‘big’ has been substituted for ‘black’ throughout, but he’s still speaking the same way, so he makes no ‘sense’ as a character precisely because he’s no longer an unpleasant stereotype.)
In The Secret Mountain, there’s an African child, Mufumu, who is a piccaninny stereotype, comic, fuzzy-haired, ignorant and unwaveringly loyal to the white saviour children, his worship of one of them (sleeping at his feet, decorating him with flowers) played for laughs.
In The Mountain of Adventure, there’s a black American paratrooper whose ‘thick lips’, ‘woolly hair’ and black face keep being referenced, and who continually talks about himself in the third person as a ‘poor n——’ who is ‘afraid of dem bad mens’.
I read these to DS and we talked about this stuff, as we did about Anne in the Famous Five, and George’s desire to be a boy being entirely understandable in a fictional world where girls are supposed to want to make the beds in the cave hideout rather than spy on smugglers. Or why the working-class child in the Five Find Outers ‘naturally’ has tea in the kitchen with the servants while others have it in their playroom, and why his manners are continually ticked off or praised by the others, and his poetry mocked.
But I couldn’t blame anyone who didn’t want to read this stuff to their non-white child.