How to set a yml sequence config value via drush cset
Uh, I love riddles like this! And finally found a way!



You first have to delete the error_handlers config key.

$ drush -y cdel devel.settings error_handlers


And then set it again.

$ drush -y cset devel.settings error_handlers.4 4


Let's check.

$ drush cget devel.settings error_handlers
'devel.settings:error_handlers':
  4: 4


Yeah! 



Just drush -y cset devel.settings error_handlers.4 4 without deleting it first would just append it and you'd end up with 1: 1 and 4: 4 both.