It can be done at the following way:
Go up to an enemy, press ` or ~ to open up the console, click on the enemy- its ID will apear after the title ''Console'' at the top of the console. Type in the id, then add in ->, then the cheat, like ''sethealth 0'' or ''setstrength 5''. For example, an annoying hoard of mudcrabs sneaks up to you- their ID should be something like ''mudcrab_00000006'', or something like that, so type in, to kill it, ''mudcrab_00000006->sethealth 0'', and poof, once you unpause, the mudcrab squeals and dies.
this is just an exapmle but it works
I hope this helps