How to automatically set "performance period" to last month in Auto Repeat?

In some countries a “performance period” is necessary on sales invoices. This refers to the period of time in which the goods or services were delivered or performed.

While this must be set individually according to the actual time period, in some cases such as recurring sales invoices it can automatically be set to the past month.

Right now we simply do this with a few variables in the customer specific terms. Which leads me to my question: How does one best trigger/set these terms via auto repeat?