We can create a Script SmartName to get the current date and time, then manipulate this to return the date x days/weeks etc before/after. We can then format the result via SmartName's Date/Time custom formatting.
Procedure
You can construct the SmartName as seen in the screenshot below - note we also use the 'Formatting Options' to manipulate the original returned value into a more legible format - retaining just the date:
The script can be cut/pasted from this text below:
var d = new Date();
var yesterday = d.setDate(d.getDate() - 1);
yesterday = new Date(yesterday).toISOString();