If I have a long scene in a cafe with a couple arguing (comedy) can I split the scene up by changing the camera angle to a couple in another corner? It is technically the same scene, but it could be broken up like this.
I would not want to step on the feet of a director or camera man, but it would need to be this specified change.
I wouldn't worry about it. If the scene cannot be shorter, then it is up to the director to break it up somehow, and that can include changing the camera angle, focusing on something else (stage business in the background, like dropped plates or something ignored by your arguing couple, or just glanced at by them).
It is the director's job to see and worry about visual impact, you don't have to do it, and you should not do it. S/he will provide any visual variety necessary if they think the camera is in the same place for too long.
If the other couple are relevant to the story this would be fine, but if they're not characters in their own right and don't reappear later, it's probably best avoided. At least some of the readers/viewers will want to know who they are, and if they suspect they were only introduced as a scene break the audience will be merciless.
If you were thinking of contrast (for example our couple are arguing their way to separation, the other couple are leading up to a marriage proposal) it could work, but you would have to visit them several times during the cafe scene - it wouldn't work only once.
For something that would break the scene without distracting the audience, something like dropped plates (Amadeus - it's an homage, honest) or a waiter asking how their dinner is going would work better. If you're going for incongruity, go full on and have someone walking past in a gorilla outfit - it'll have the audience scratching their heads but they're more likely to find it quirky than being annoyed by characters they might or might not need to care about.
In a story, you can do anything. :/
Whether it's good is another story. And whether cutting to another couple is another story is itself the story of this decision. Are you cutting because the primary story isn't engaging? If you are, that is the real story here: you need to tell a more interesting story. Cutting away may be avoiding the issue and having it worse. If cutting away reinforces your story, in an additive, smooth way, then it may be just what the scene needs.
Ideally, most things in your story are additive and matter. What you have here is a story-smell. In programming it's called a code smell. Something doesn't smell right to you. It's worth taking a closer look and looking at all of the tools in your toolbox. It may not be what you initially think it is. Long is the adjective coming to your mind, but it's likely not the root cause.
What do you think the problem is? Is it self confidence, boredom, weak dialogue, or lack of progression? Something else? If you don't know, run it by done friends.
