Hello Alex!
The video editing for h.265 works the same way as for other formats - with frame accuracy editing mode 99% video data remains unchanged, only few frames could be re-encoded, with K frame accuracy there is no re-encoding at all (you can set the accuracy at "Control / Frame Accuracy (Smart mode)".
Maybe have you noticed some artifacts after the editing? If yes, could you please upload the original inlut file as well as the project file from Video Splitter to any file host service (e.g. Google drive) for we could reproduce this problem at our end?