Thank you all for the fast responses. I knew it is not possible for "normal humans" to change the displayed name (indeed, username is different than profile name), unless you become VIP.
This is why I asked also about posting such an emoji in different profile fields (such as social media fields). So you just copy/paste the code from links as ones provided by mk4 and mersal? As a issue of note, on mobile I don't get any code for any emoji from either one of both sites; I will try also on desktop.
@Ddmr: than you for that link. I found funny the fact that in the respective thread the example was also about TF
However recently I saw someone having an emoji at his profile in one of the social media fields and that made me curious.