The Grand Inquisitor might interact with Anakin Skywalker. This would be really interesting as Anakin is on the verge of turning to the dark side during the Clone Wars. The Inquisitor could try to nudge Anakin further towards the dark side, or Anakin could sense the dark presence in the Inquisitor and be suspicious of him.
One of the main themes is the conflict between faith and freedom. The Grand Inquisitor represents a certain view of religious authority that restricts individual freedom in the name of faith.
The common people in the story are also important. Their reactions to the Grand Inquisitor and Christ, and their acceptance or rejection of the ideas presented, help to drive the story's exploration of themes like faith, power, and freedom.
One possible motive could be to gain more power. In the Clone Wars era, there are many opportunities for someone with his skills to manipulate the situation. He could try to amass power by influencing key players on both sides of the war. Another motive might be to study the Jedi at their peak. He was created to hunt them later, so understanding their ways during the Clone Wars could give him an edge in the future.
If the Grand Inquisitor travels to the Clone Wars era, things would be very different for him. First of all, the technology and the state of the galaxy are different. The Jedi are more respected and in a position of power. He would probably be seen as an oddity or a threat right away. His presence could disrupt the balance of power between the Jedi and the Sith in that era. He might try to use the Separatist movement to his advantage, maybe by influencing some of the leaders to target Jedi specifically. But the Jedi would be on high alert, and his every move would be closely watched.
The Grand Inquisitor could be on a mission to study the Jedi during the Clone Wars for future reference in hunting them down. He might infiltrate the Jedi Order undercover, observing their training methods, their weaknesses, and how they interact with the clones. This would give him valuable insights that he could use in his later role as an Inquisitor, but he also has to be careful not to be discovered by the Jedi during this time.
A possible character for the High Inquisitor could be a long - lost relative of Dolores Umbridge. They might share her strict and often cruel approach to discipline. This character could have been in hiding for years, secretly observing Hogwarts from afar and waiting for the right moment to impose their own version of order.