Acestar13 said:

I have watched many youtubers show clips of raid. A  lot of them when they equip a character with an artefact it tends to change the characters looks, is it an actual thing in-game.

No, it doesn't work that way.

But I have good explanation of what you may have seen. We have many reskinned champions (a good indicator of how careless Plarium is about their game and how low they think of their audience) and switching between those may fool you there is a actual change of characters appearance when equipped differently. Try to rewatched those video with that info in mind and pay attention to names of the champion, that will clear things up.