True… If Gramps has a steep learning curve, SuperTool has a vertical wall.
But in this case, it is just 3 lines & 2 options
[initial_statements]
from gramps.gen.datehandler import parser
[statements]
my_date = event.get_date_object().get_text
event.set_date_object = parser.parse(my_date)
With the “Selected objects” and “Commit changes” selected.
Then I would find an Event to test (note the Event ID & date) and execute the script.
If it works, process in batches. There a table display limit of 1,000 records somewhere, Python or GTK. So that’s the biggest batch you ought to process.