You can do this, but it won't be a permanent tag. And it will only work for you. Everyone's elses tag won't change.

You can add an animation to your pspBricker.txt.

Go to BakonICE, switch your animation to the animation that you want your clan tag to be. And press SELECT to switch it from Name to Clan Tag. But it doesn't show up on your clan's clan tag. Only your clan tag.