What are the requirements for a header for an open passageway through two rooms?
It's almost surely possible but how much will you have to modify?
Let's assume a structural header is required.
If the header is already high enough, nothing might be required, just remove cripples. If the header is not high enough you may still be able to do this. You might raise a header into the attic and the use hangers to support any beams. Supporting posts would need to be installed to support the new header.