Explanation:

Why Option B is Best:
Mass Quick Actions allow bulk updates directly from list views, making it efficient to edit up to 75 cases at once.
How It Works:
Create a global Quick Action for the "Case Type" field.
Select multiple cases in a list view and apply the action in one step.
No Code Needed: Configured via Setup without requiring macros or shortcuts.

Why Other Options Are Not Ideal:
A. Run a macro on each case – Macros automate individual case actions (e.g., pre-filled replies), not bulk field updates.
C. Keyboard shortcut – Shortcuts speed up navigation but don’t support bulk editing.
Reference:
Mass Quick Actions for Bulk Edits:
Create Quick Actions
Update Records in Bulk

Conclusion:
For scalable bulk updates, Option B (Mass Quick Action) is the most efficient solution. ✅

Implementation Tip:
Combine with list view filters to target specific cases (e.g., "All Open Cases").
Use Screen Flows for more complex bulk updates if needed.