Hi Colleen, As long as you have good and justifiable reasons for it – e.g. “the original calendar was wrong, and this one better reflects our plan going forward” – then it should be acceptable to anyone focused on an accurate schedule forecast. If a calendar change reflects a revised management approach, then be prepared to fully document what that change entails and why. In case of future schedule claims this may be a key piece of evidence either way.
Some “gotchas”: 1. Project resources automatically adopt the project calendar in effect at their creation as their base calendar, and they keep that same base calendar after the change. Differences between the old and new calendars may not be reflected in resource-loaded tasks. 2. The forecast schedule will change according to differences between the two calendars. If you have existing baselines, then the variance analyses will be affected.