Depends, some vehicles require a good bit of disassembly to get the headliner panel out. A and B and C pillar trim, sunroof stuff, if you have crazy stuff like overhead video players or ,moon/sunroofs, the complexity level could rise. Assuming, of course, it uses a pressboard panel like many modern ones do. Older cars like the old Cougars and Mustangs, some of them used a fabric sheet supported with steel tension bows through loops in the back.
All that said, if you can get the panel out, the actual piece of removing the old liner fabric and replacing it is pretty easy.