[dejongj]

How I normally do that is indeed by having predecessors defined (or dependencies as Omniplan calls them), that 1) allows for highlighting the critical path, but also when you have a milestone date that 'starts' it you only have to change that date and everything else gets 'rescheduled'...

I think that from a project management perspective that approach makes sense, as it is a pretty big decision to make to shift everything, so worthy of a mile-stone!