Changing shapefile's field type using fiona?

You can automate it with geopandas, but there seems to be an issue in automatically converting the pandas datetime objects to the right properties schema. Fortunately, as geopandas is built directly on top of fiona for reading and writing you can specify a schema for writing output, e.g.:

schema = {
    'geometry': 'Point',
    'properties': {
        'npri_id': 'int',
        'facility': 'str',
        'year': 'datetime',
}}

geodataframe.to_file('output.shp', schema=schema)

Note that the number of fields in the schema must match the number of fields in the geodataframe to export (though you can of course subset the fields to export).