The way I see it is that there is no functionality in the CA PPM GUI which would allow editing of baseline details.
It used to be possible to use Open Workbench and step back the actuals and ETC until you got to a specif situation in the past and modify the dates. Then you could create a new baseline at that point of time of set the baseline for a view or selected tasks. Then you would re-enter the actuals until you got back to the current state. However, if you have entered actuals through timesheets it is no longer possible to switch the track mode for entering time in OWB. So this possibility no longer exist.
Even earlier it was possible to edit the baseline directly in OWB by setting the entry for that in Windows registry. Currently that does not seem to work either.
What I have used recently is a gel script which reads the current data and XOGs in a new baseline. Based on that. It should be possible to create a baseline with any given data.