This is a bit general question but can one edit directly the output like in Mathematica? Because one may want to apply a command to a part of the output, or to copy and paste to the output.
No, you can't, but that's a deliberate decision, as cutting and pasting makes your notebook very unreproducible (you cannot change something at the top and have the effects of that change automatically propagate to the remainder). But there is a better (IMHO) way to do something with a similar effect. I have started writing something more about this a chapter of the new reference manual, see
https://cadabra.science/notebooks/ref_selecting.html
Thanks, Kasper. This is really good to keep in mind. Zooming function would be helpful if one wants to deal with simplifying the Gamma matrices using the chirality of spinor with \Gamma_{11}, for instance.
Can you give a bit more detail about what you want to do in that example? (is there anything missing in zoom that would be helpful?)
zoom
I will send you some image attached.