Premiere Custom Dip To Black Transition
This is a surprisingly tricky question, as Premiere doesn't let you edit transitions like, say FCP does.

One way of doing it is to use presets:

First create a preset for your fade in. Set two opacity keyframes for your fade-in then in the Effect Control panel right click on the Opacity effect and choose Save Preset:



call it fade-in or whatever and choose Anchor to In Point, so that it will apply it to the start of the clip.



Then on a fresh clip with no keyframes do the same for your fade out, choosing Anchor to Out Point in the dialog.

Now you can apply both your presets to your clips to create your fade out / in, and the good thing is that the presets will add new keyframes without deleting the existing ones, so the fade in won't overwrite the keyframes of the fade out. Tip: you can select both presets in the Presets folder in your effects window by holding down Command / Control, then you can drag them both to a clip at the same time.