Trying to do a simple overwrite edit in the primary storyline seems to be needlessly long winded. For example, if I have added a shot to a sequence, but later decide I want to replace it with an alternative option. By default X seems to be intent on performing a ripple insert, when what I'm looking for is a simple Overwrite. I hope this is possible and I am just missing a trick...seems like a pretty glaring omission if not.
Obviously it's simple to remedy...delete the following clip so the timeline snaps back to where it should be/insert as connected clip and then drag it down into primary storyline...but that's pointless extra steps.
D is the shortcut for an overwrite edit. However, if you looking to replace one clip with another, I recommend using the Replace Edit which can either replace a clip at the same length as the original (OPT+R) or replace using the length of the new clip (SHIFT+R). Just select the clip you want to replace first.