Over the four seasons of Preacher, we are given a pretty good idea of how Genesis works and what it can and cannot do:
Genesis is not a genie and cannot just bend the reality according to its host's wishes. It only affects intelligent beings' minds to make them obey to verbal commands of the host. Affected persons execute the command immediately and utterly.
This comes with pretty logical restrictions related to verbal commands:
The person must be able to hear the command. Being deaf or using earplugs makes one immune to Genesis powers.
E.g. the Grail successfully uses military grade ear protection when confronting Jesse Custer, or brings in a deaf person to be able to communicate with him without the use of spoken words.
The person must be able to understand the language in which the command is spoken.
E.g. when Jesse commands the two cameleers to reconcile, one obeys and the other does not because he does not speak English.
The person must be able to execute the command.
E.g. when Jesse orders the badly hurt pilot to not die, he dies anyway, because it's beyond him to stay alive at this point.
With that being the case, how could Jesse send Eugene to hell by ordering him to "Go to hell"? Was it clearly not within the boy's power to execute that command?