Drupal 8: To run a mymodule_update_8004() multiple times in development enivrements use these queries:

hook_update_N.txt

SELECT * FROM key_value WHERE collection="system.schema";
UPDATE key_value SET value='s:4:"8003";' WHERE collection="system.schema" AND name="mymodule";

How to "revert" a custom module's update 'N value'
D7 only: If you need to execute an update hook another time when testing it locally you can "revert" a custom module's update 'N value' with:

UPDATE system SET schema_version = [last_successful_update_ID] WHERE name = '[name_of_module]';
Replace the square brackets plus its content. See https://drupal.stackexchange.com/a/69841/19480.

Examples:
SELECT schema_version FROM system WHERE name = 'alpha_sierra_main';
UPDATE system SET schema_version = 0 WHERE name = 'alpha_sierra_main';
UPDATE system SET schema_version = 7000 WHERE name = 'alpha_sierra_main';

Using drush through a Drupal API function, both valid for D7 and D8:

drush ev "drupal_set_installed_schema_version('[name_of_module]', [last_successful_update_ID])"
Or you could install the drush uroll module and do

drush uroll --module=[name_of_module] --version=[last_successful_udpate_ID]