You can simply use GM command '/pc giftonline [itemID] [stack]' to get the horse vouncher, like this one:
Horse Voucher: PC Cafe Only (White) - Black Desert Database 1.0The itemID would be 50115, then you would get a horse.
You can modify the database by using Robo 3T software to has all the horse skill, the horse table is in [gameserver] -> [servants]. If you already has a horse in your character then you would see your horse name in on of these servants data.
The horse skill value is in [servantSkillList] -> [servantSkills], you can simply modify the content by clicking RMB on [servantSkills] Key --> [Edit Document], it would show up the Json format text content, just edit the value inside it.
Horse skill ID is stored in horse information page:
Horse - Black Desert Database 1.0
Click the 'Posible skills' button to show those horse skill, move your mouse onto one of these skill's small avatar then you would get a hover tooltips menu that tell you what ID it is, that is the ID which is stored into [servantSkills.skillId].
Hopefully it would help you.