Hi Motosep I've tried to show what Mkdm was describing in the attached images.

1) Start with a curve on the geometry of interest, make sure it has curved corners to some extent as sharp changes lead to artefacts. A simple way to do this is to use the Curve - > project function to transfer a rounded rectangle onto the geometry

2) Draw a small curved shape such as a circle or rounded rectangle (again sharp edges lead to artefacts), see bottom of picture, and use Sweep function to generate temporary geometry. I've exaggerated size in example image to make easier to see.

3)Subtract temporary geometry from main object to generate cut line using Boolean -> Diff function and you have your cut line.

The final two images show a finer size of cut line generated using a smaller rounded rectangle for the sweep in moi and rendered out as an example of the effect

Cheers
Andy