Is it possible with xslt to take a date field and subtract N number of days from it? If so, can you please provide me an example?
Yes, with XSLT 2.0 it is possible, and very easy to do.
There are a lot of Date/Time/Duration functions in XPATH 2.0, which are part of XSLT 2.0.
This example subtracts 1 day from the date 2010-01-01 to produce 2009-12-31: