It's the release manager's responsibility to update the version
number in Misc/NEWS. As I finish up 3.5.0a3, I will be changing it
to say "What's New in Python 3.5.0 alpha 4?". And I will change the
release number in patchlevel.h to say "3.5.0a3+". I don't know why
it is this way, but that's the way it is, and I assume there's a
good reason for it.
Since you don't have the 3.5.0a3 changes yet, no, it's not correct
for you to put "alpha 4" into Misc/NEWS. Doing so would trip me up
a little.
The release process is mostly automated, although there are manual
steps where the RM is guided through the process. Fixing up the
heading in Misc/NEWS is one such manual step. FWIW, I have in the
past bungled a release so badly that I missed making this change. I
was happy to discover someone else had fixed it for me. So I'm not
saying "nobody but the RM should ever touch it". But maybe you
should wait a day or two after the release comes out before you
start up your text editor.