Several workpieces can be clamped depending on the bed length by using interchangeable slides;these interchangeable slides are installed without tools.

interchangeable mechanical slides

de Luikerwaal
https://www.luikerwaal.com › bewegend2_uk
29 Apr 2024 — Each composite lantern slide consists of two round outer slides and one square inner slide held in place by an easy-to-use spring clip. The base ...

I think they are talking about a piece that goes in the middle of the clamp, in a system like these
https://hyquip.co.uk/vertical-and-horizontal-machining/3890-...
https://hyquip.co.uk/vertical-and-horizontal-machining/3879-...

In this video https://www.youtube.com/watch?v=vPhIshW41Hk it's just described in the voiceover as a Mittelbacke but in the text below the video as a Wechselschieber

Here's another English example with "double-sided wedge clamps"

https://norelem.co.uk/en/Product-overview/Clamping-technolog...

At about 1:20 mins in the video here - https://www.kohn-spanntechnik.de/english/ - you can see that the Wechselschieber serves to allow the vise to clamp two parts instead of just one (if the vise opening, the Bettlänge, is large enough relative to the size of the parts to be held) i.e. convert a single-station vise into a double-station vise. This intermediary jaw is known as a 'floating jaw'. Here it is attached simply by inserting and swivelling, making it a 'quick-change jaw'. This notion appears as schnellwechsel in German; I assume the notion of celerity is contained in Wechsel alone and can be contained in 'floating' (certainly in the video below, the 'floating centre jaw' works exactly the same way as your Wechselschieber.

The systems are comprised of an array of unique floating jaw plates that fit between and interact with the existing movable and fixed jaw plates of the vise.
https://www.mmsonline.com/products/workholding-system-capabl...

'Floating centre jaw' in video here - https://www.youtube.com/shorts/_8p7yb_mc8U

So '(quick-change) floating centre jaw'.


--------------------------------------------------
Note added at 2 days 18 hrs (2025-04-20 23:42:21 GMT)
--------------------------------------------------

Your text appears to be from Kohn whose product - see page 122 here - https://www.cnctools.ch/wp-content/uploads/2022/06/KOHN-Kata...
is referred to as Kohn Wechselschieber für Mehrfachspannung, https://www.cnctools.ch/werkzeug/02410030-kohn-wechselschieb...
though their own site calls it a 'changeover slider', which stinks of 'translation' in the worst possible sense.
https://www.kohn-spannwerkzeuge.de/zubehoer-kategorien/wechs...