Hello and thank you for your fast reply.
Exporting all the files as FLAC might be time-expensive.
(I could use Audacity's batch, though.)
My other idea was to check the HEX codes of the wav files,
but strangely, I could not find any tempo information.
Tempo 197 should be C5, but there was nothing...
Anyway, I think the (wrong) tempo information won't be a problem at all.
I use Kontakt 5, paste my desired samples inside of it and save it as nki + Studio 1 preset.
When playing the sounds with Kontakt 5, it doesn't matter what the project BPM is - they always sound the same.
So I think I can live with that small issue.
But if anybody knows how to change the wav tags, s/he can feel free to post it.
Thanks anyway!
Edit
I just have to be careful when exporting the wav files.
If I change the BPM and then export a wav file, it will sound different when adding it in Kontakt 5.
For this reason I set the tempo to NONE (even though it's not valid anymore when importing the wav file again.)