stefaan wrote:What I'm looking for is the possibility to mark/select a region (for instance because I want to replace it),
If you know the exact start and end of the part that you want to replace, you could select it and then "Edit menu > Clip boundaries > Split".
However, the way that I would do it is to roughly mark the region that I want to replace with a region label (just quickly and approximately), then select and copy the bit that I want to replace it with, and paste the copy into a new track, roughly where I have marked with the label. Then I can delete the label track, and use the
Time Shift tool to accurately position the new clip in the correct place below the part that I want to replace. Finally, "Split delete" the part to be replaced, leaving a bit of overlap to make short crossfades from one track to the other and back again.