Change due dates in a subproject by a defined increment

I have a series of subprojects within a main project, each with a set of tasks. Sometimes the subproject’s due date changes and so I have to change the tasks’ due dates as well, except there is a variety of dates (e.g. 1 week before subproject due date, 3 days before…, etc.) I can’t just select the whole subproject and click on, e.g. +1 day or +1 week because it sets all the dates to the main due date of the subproject. Is there an automation or command or plugin that will let me change the due dates of a set of selected tasks/projects by a defined increment?

I use a Defer script that allows you to select items and then add a user-specified number of days to the Due and Defer dates. It was created by Dan Byler in 2011 but it still works with OF3 in Monterey. And with a bit of Googling, I found that he renamed it Shift, and it’s available on Github: GitHub - dbyler/omnifocus-scripts: Scripts for use with OmniFocus