A few months after I got my Hobonichi planner and cover, I decided I needed to personalize it. The cover was already a distinctly TARDIS blue so the solution seemed obvious. I found some artwork online, resized it in Photoshop. I printed it out, trimmed it to size and then slid the artwork underneath the plastic sleeves. No adhesives were used so the cover was not damaged in my customizing. If I ever feel like removing the TARDIS art, it would just mean removing the plastic covers and pulling the art out. Easy Peasy.
Go for the Hobonichi Techo love, stay for the awesome idea behind her TARDIS cover.