How Damaging To 'Chrome Film Is "Re"-Reloading and "Re"-Readvancing?

[DF]

I forgot to mention after my splishy-splassy mishap I rewound Ektachrome early from the 27th frame to clean water from inside camera.
I'm certain no water got into the roll. Nevertheless, to put it back into the camera rapidly shuttering away till 27/28 seems it could be in some way
detrimental to the roll being color transparency.
'Done this before with B&W print film but no noticeable problem.

 

[MattKing]

Back in the day, the operators of the semi-automatic slide mount machines in the Kodak Kodachrome labs used to hate you for doing it ).
They had a standard insert which was returned with the developed and mounted slides explaining why one or more slides either couldn't be mounted or were sliced down the middle!
Operating those machines must have been mind numbing!

 

[koraks]

'Done this before with B&W print film but no noticeable problem.

Slide film won't suffer in any different way, or more so than B&W.

The only concern I'd have (but it's marginal) is that sand somehow got onto/into the felt light trap. If that's the case, you could end up with longitudinal scratches on the film.

 

[BrianShaw]

Is it really worth doing? Might be better to process the film and be thankful it wasn’t damaged.

 

[abruzzi]

I used to do it all the time. The Pentax MZ-S can treat 135 casettes like film backs--rewind and leave the tongue out, then when reloading auto advancing to the next frame (it didn't remember the frame, but when I rewound, I'd use a small sharpie to write the frame number on the tongue, then you had to dial the number in when loading.) I'd use it to hop between 1600 speed film (night) and 100 speed film (day) while traveling. I frequently used E6 film in the camera.

 

[Taylor Nankervis]

Swapping in/out rolls is standard in professional practice, at least back when 35mm ruled, and much of that film back then was destined for the front covers of magazines, as mine was throughout the 1990s up until 1998.

In the case of your question, loading, unloading and reloading any film is as normal as getting up in the morning! How do you imagine there is harm in this?

True though, it's tedious and requires a clear head to record notes of where you left off in the roll, and of course marking the roll as "P/E #n" (part-exposed, with #n being the next frame number) of "EXPOSED" is essential. I don't often use 35mm now, but the 'switcharoo act' was very common when 35mm was my only format (20+ years ago), as many as four rolls in one day to suit conditions.

There is no harm whatsoever, however imagined, to the film, be it negative or chrome. Just ensure you make a note on the cassette of where you left off when it comes to reloading.
I would be less certain about water not having entered the cassette, and more about the detrimental effect of water within the camera. This is how rust starts.