The direct answer is No and No --- Both the Python API and the C++ AddOns do not have access to schedules or their data -- at this time.
However, you can indirectly access the schedule data (any schedule) by exporting the schedule to a excel spreadsheet file . Then use Python to access the spreadsheet. Python has several extensions that access Excel files.
The problem then is to get the modified data or spreadsheet back into Archicad schedules and again there is no way to do that -- other than to just just take a screenshot of the new data table and paste that into Archicad as a png file (etc.).
Direct access to schedule data is a often asked request, but mostly ignored by Graphisoft. I assume as part of Graphisoft's new policy of closer Customer relations