Is there a way of changing an entity's death message / inventory name using script?

[cerulean badge]

I have a tameable entity using horse's runtime identifier. That means its inventory name will display 'Horse', same will happen to its death message once I kill a tamed entity that has not a nametag. Is there a way of accessing death messages/inventory titles using script and then be able to change it?

[blazing saddle]

I did it by turning showdeathmessages gamerule to false, detecting the deaths and sending my custom messages using worl.say (now sendMessage I guess)