Some can be. If they are rare or limited edition, they can have a higher value. For example, if it's a chase variant or a figure that was only made in a small quantity, collectors might be willing to pay more for it.
To open Funko Pop comic covers, first, inspect the entire perimeter for any obvious opening points. It could be a small button, a slit, or a flexible part. Apply gentle pressure or manipulation at those spots to unlock the cover.