On a scale of (perfectly ok) 1 - 10 (Never) - How bad is it to change activity ID's on large projects...I am reviewing a large project and the contractor has changed 500 of the 2200 activity IDs. I is a job that they are strugling with creating a schedule for and there are constant and many changes. They are changing the ID's to follow their revised WBS. I personally would never embed codes in ID's for this reason, its fine if you re-do the same type of work, but not for quick new unique schedule developments. The reason why I feel it is "9" is because you cannot compare to baselines or prior months (easily). Before I tell them they have to put 500 activity ID's back I thought I would ask the community their opinion - what your opinion? (ps, it has negative float, thus a re-baseline is unlikely - which might be the only way it could be allowed.)