Can I cancel a comic preorder?

Yes, any time before the order cutoff shown on the product page, for a full refund. After the cutoff the order has been placed with the publisher and cannot be cancelled.

Star Wars: The Original Marvel Years Omnibus Vol. 2 Gene Day Cover [New Printing] — PREORDER

Name: Star Wars: The Original Marvel Years Omnibus Vol. 2 Gene Day Cover [New Printing]
Brand: Marvel Universe
SKU: C5-PO-9781302972929
Price: 100.00 USD
Availability: PreOrder