From help:
>Yes, edit one of your milestones to the right date and check “Yes, shift future milestones too.” For example, check the box and move a deadline out 5 days and Basecamp will also move all future milestones out 5 days as well. This also works when you move milestones forward. Selecting “Keep shifted milestones off weekends” will move milestones that land on a weekend forward to Monday.

Does this mean that all future milestones in THIS project will be shifted or ALL future milestones in ALL projects?

Sure it’s the former but want to check before I do it.

This project.