If using HDR to re-grade an old film, then they are usually working from the neg, not prints, and current scanners are able to capture the neg without the need for multiple transfers.

You are right in that the original grade for older movies is totally different to what you could do with a HDR grade, and anything is revisionism really when making a home version, all home versions are radically different to the cinema version, regardless of whether HDR or not.

However, exactly what the grade is, is up to the colourist. You could do a totally new grade to change the experience into something completely new, or you could use the wider colour gamut, and finer colour detail of HDR to create a home version of a movie that is closer to the original cinema release than ever before

It is up to the people using it, their skill and intention. It is a huge step forward in visual fidelity and brings the recorded image much closer to reality. What directors and others choose to do with the tools is another thing altogether, but it can certainly be used to make versions of films that are more true to the originals.