Considering you have successfully installed the rageHookPlugin,
just unzip this archive in your rdr2 main folder (typically C:\Program Files\Rockstar Games\Red Dead Redemption 2)
Added some safety check but i think crashes come from RageHook
In real life you won’t steal a horse by error. SAdly in Rdr2 you got no key to say mount my horse. Now you do.
Once on your horse set it as your main horse by pressing T (key can be modified in option file).
You will never mount anything but that horse by pressing T (E keeps on working as in vanilla game)
To change this mod options just edit the c#Plugins\MyHorseKey.opt file (with a text editor, notepad for example) within your read dead redemption 2 main folder (typically C:\Program Files\Rockstar Games\Red Dead Redemption 2)