 Here is the Python code based on your instructions, using the Basilisk library:

```python
import Basilisk as bk
import sys
import os

def rerun_monte_carlo_simulations(scenario_name, num_processes, run_numbers, retention_policies, archive_dir, disperse_seeds, execute_count):
    bk.setShouldArchiveParameters(disperse_seeds)
    bk.setShouldDisperseSeeds(disperse_seeds)

    mc_controller = bk.MonteCarloController()
    initial_conditions_dir = "initial_conditions_directory"
    mc_controller.setArchiveDir(archive_dir)

    box_and_wing_params = bk.boxAndWingParameters()
    mc_controller.addToSpacecraft(box_and_wing_params)

    for policy in retention_policies:
        mc_controller.addRetentionPolicy(policy)

    mc_controller.setExecutionCount(execute_count)
    mc_controller.setICRunFlag(True)

    mc_controller.runInitialConditions(initial_conditions_dir)

    run_subset = mc_controller.extractSubsetOfRuns(run_numbers)
    mc_controller.addRetentionFunctions(run_subset)

    mc_controller.run(num_processes)

if __name__ == "__main__":
    scenario_name = "my_scenario"
    num_processes = 4
    run_numbers = [1, 2, 3, 4, 5]
    retention_policies = [bk.RetentionPolicy.AVERAGE, bk.RetentionPolicy.STDDEV]
    archive_dir = "archive_directory"
    disperse_seeds = True
    execute_count = 1000

    rerun_monte_carlo_simulations(scenario_name, num_processes, run_numbers, retention_policies, archive_dir, disperse_seeds, execute_count)
```

This code defines a function `rerun_monte_carlo_simulations` that takes in the scenario name, number of processes, run numbers to rerun, retention policies, archive directory, whether to disperse seeds or archive parameters, and the execution count. It sets up the Monte Carlo controller, specifies the initial conditions directory, the archive directory, the execution count, and whether to disperse seeds or archive parameters. It also adds the specified retention policy and run the initial conditions. If the function is run as the main program, it calls itself with some default parameters.