now.get<b>unit</b> returns a number. 1-31 for day, 1-12 for months. Just use those variable instead of the clunky now.getDate() and add or subtract directly.
For example:
If you want to show one year ahead, 2 months behind and 8 days ahead, you'd change
Code:
document.write("Today is " + dayName[now.getDay()] + ", " + monName[now.getMonth()] + " "+now.getDate() +".")
to
Code:
document.write("Today is " + dayName[now.getDay()+8] + ", " + monName[now.getMonth()-2] + " " + now.getDay()+8 + ", " + now.getYear()+1 +".")