Select a modification in hg diff

with

hg diff  

mercurial show me the modifications, separated by @@.

I can get only one of them?

If you are on Windows, I would recommend installing TortoiseHg and using

hgtk status

The modifications separated by @@ are named "patch hunk" or simply "hunk". You can use the record extension (disabled by default).

You can pipe the output of hg diff into a program like filterdiff to further refine the patch.

On Ubuntu, try the hgview program. It has a pretty nice interface.