Which files need to be modified to replace all "News" entries against "Blog/s" in English language.

You would have to modify the theme and possibly function calls. It is the default used everywhere.

To rename the "news" in the url use the rewriteToken plugin.

Uff - this sounds like work.

"You would have to modify the theme and possibly function calls. It is the default used everywhere."

Could this be changed in a future release?
I would think that ZPC-users want to be flexible...

"news" is not always hardcoded but some function offer different names as parameters. You really have to look at the theme you use where it is to be changed. Using a good editor or IDE like Netbeans helps a lot to find this.

I generally tend to avoid add more options, especially since the demand was not that high so far.

If you use Zenphoto in another language, you could also customize the translation. For example in German it becomes "Neuigkeiten". We on purpose didn't call it "blog" actually ;-)

When using "find" then so many files were displayed where the searchword "news" appares - that I got scared to do something wrong and mess up the app...

It really depends on the theme used. "news" is also used internally as a keyword, not all is display. Best review each theme page of the theme used and start looking there.

However, I will take a look if we can add an option for this. But if we do it still might not work everywhere if it is not used as themes (and plugins) can always choose to override. That's always the curse of prebuild themes ;-)

/zp-core/zp-extensions/zenpage/zenpage-template-functions.php

I replaced
gettext('News')
against
gettext('Blogs')
and things look good now.

Don't know yet if I want to replace "news" in the url as well...

You have tried to do this modification on your theme, right? ;-)

Honestly: I've replaced it where ever I found it!

The change was visible after editing this core file - all other changes in all other files before that had no effect on the front end.

Well, I had to mention it ;-) And as said we consider making the visual term "news" an option. It's on the list so no "hacks" will be necessary.