Two users of mine have reported it's possible to register multiple times for the same tournament:
The participant_id is different on those last two entries, but it does show them there twice. Looks like if you just append /register to the tournament URL, it will register you again.
Code:
[12:55:52] [root] [~]$ mysql -e "SELECT custom_value FROM fightnite_xf.xfa_tourn_participant WHERE tournament_id = '4';"
+-----------------+
| custom_value |
+-----------------+
| BraidedWeb74737 |
| iiShibui |
| iiShibui |
+-----------------+
The participant_id is different on those last two entries, but it does show them there twice. Looks like if you just append /register to the tournament URL, it will register you again.