[O] Shortcuts for setting or changing the warning period "-3d" in DEADLINE timestamps?

[Martin Beck]

I often use individual warning periods for defining how many days before the
DEADLINE the task will show up in my agenda like

DEADLINE: <2013-02-27 Wed -3d>

However, it seems not to be possible to enter this warning period directly when
defining a date with the calendar e. g. by C-C C-D.
Is there a syntax to enter warnings here directly?
If not, could it be defined, please? :-)

IMHO it would also be helpful to have a shortcut to directly modify the warning
period of an item with a timestamp in the agenda. (like it is possible with
Shift+Left/Right Arrow to modify the date day by day).

Kind regards

Martin