I want to modify some of the code and UI of the DICOM module, but when I click Edit, a py.exe appears and then disappears. When I click Edit UI, error: Application does NOT exists [E:/Company/SlicerBuild/Slicer-build/bin/D:/Qt/5.15.2/5.15.2/msvc2019_64/bin/./designer.exe].
Slicer gets an incorrect path.
Yes, you can do that for modifying your local installation or experimenting. If you want to make improvements to the UI or add hooks to more easily support alternate use cases please consider making contributions to the slicer repository.