Possible To UPDATE Multiple Fields Conditionally?

I have a am doing some date calcs () . The situation is that I have a Move date (date a customer moved to a new home). I want to calculate their sales for the following 0-3 months after the move (month 0 being the move month). I have the month and year of the move (MthStart, YrStart), and I am adding 3 to MthStart to get the MthEnd of that 0-3 month period. I will then find sales BETWEEN YrStart&MthStart AND YrEnd&MthEnd (there is a YrMth field in the sales table)

Of course, for MthStarts 10, 11, and 12, the ends are 13, 14, and 15. So for these, I need to subtract 12, and increment the YrEnd by 1.

I am wondering if there is a way to update both the MthEnd and YrEnd fields at one time instead of separate SETs (or maybe I am just thinking about this the hard way to begin with). Is there a way to update both in a single CASE statement like WHEN MthEnd> 12 THEN MthEnd-12 AND YrEnd+1?

Code:
CREATE TABLE #myTable (
YrStart INT,
MthStart INT,
YrEnd INT,
MthEnd INT);

[code]....