It might help if you give more detail about your situation. Where do you get these files that are 4.096x faster than normal speed?
The only time I have ever heard of PAL (25fps) media being “fast” is when it is converted from original 24fps film. Some conversion processes will run 24fps file at 1.04x speed to create 25fps PAL. Other than that, any PAL media that was originally produced at 25fps will already be at the correct speed.
If the thing you are trying to do is “undo” the 24fps film conversion which I described above, then the speed is 4% fast and you need to slow it down to 0.96x. Here is my suggested workflow to do that:
Set the video mode (Settings->Video Mode) in Shotcut to a 24fps mode. For example, “HD 1080p 24 fps”. Or create a custom video mode. Just make sure the video mode frame rate is 24fps.
Open the file you want to convert.
In the Properties panel, set the speed to 0.96x to slow down by 4%.
Encode the project - make sure the “Frames/sec” field is set to 24.000.
If your situation is different than what I describe above, then please provide a better explanation. Particularly, show the math explaining why you need 4.096x speed.