[Orgmode] Changing multiple dates en masse

[Mark Elston]

I teach a weekly class and have a number of tasks that
go into preparing for the class.  I have an org file set
up with these tasks.

Occasionally I have to put off a class for a week.  That
means all the following classes and their sub-tasks must
also be moved by a week.  So far, I have had to expand the
entire tree and visit each task in turn and use the S-right
on each date to get the rescheduled time correct.

Is there a way to select a region and have org-mode add an
offset to each task (specifically the deadlines) in the
region?

Alternatively, is there a way of specifying my tasks such that
I can say that Task A is to take place 1w after Task B, or Task
C must take place 4d before Task D?

Mark