The actual work of recording a record or making a film just requires that you consciously block the time out to do that and nothing else. That's what I do.
I'm not sure why writing for others became harder. Probably a reluctance to give away anything you might conceivably use yourself caused a block. I did it, but it remained hard when it had once been easy.
On 'Sin Nombre,' Adriano Goldman and I improvised a lot of things on-site. We were working with untrained actors, and you can't really block a scene in a traditional way.