How do I associate a pre-registered tournament player card with my HiveMind account?

Linking your tournament player card with your account (see Player Card Registration) will also link the tournament player to your account, and retroactively link all its games to you.

Is there a way to set up different rules for different parts of a tournament stage? For example, best-of-5 for most of the stage, with finals being best-of-7?

Currently this is supported with a workaround. When editing a stage, the new rules do not apply to any completed matches. Editing the stage before the finals round will only apply to future matches.