I tried that, the changes still did not take...

btw: what is best, altering CoreResources or CoreImprovements? or i need to do both?

OK, stupid question.  I'm sure you have done this, based on your references to files in the original post, but sometimes it gets missed.  You did check 'use mods', correct?  There's always the chance the last patch or whatever may have toggled this, so it's an easy thing to check.

Also, make sure you back up the appropriate file before replacing anything in the root directory.

As mentioned, you do need to start a new game to see changes ingame, as the save game saves the current state of the .xml files for your scenario when you start that scenario.

Another thing that happens is that if you don't have your tags just perfect (i.e. proper syntax, open and close symbols <>, etc.) the game will ignore any files in between the missing brackets and such, and your change won't take effect (defaults to the original file).

It's easy to accidentally delete a character when you are modding files, and it can be a bear to track them down afterwords.  Hence why I practice the 'baby steps' philosophy whenever possible, so that I at least know which change may be hanging me up.  Again, it isn't always obvious, but it helps. 

Of course, I code in notepad usually, so I don't have an .xml editor to point out issues.  In the past, I've had spacing/character issues that have wigged out my .xml using an editor (which effectively damages the file), so I don't use the .xml editor anymore.  Railroads was REAALLY sensitive to this, but I don't recall having any major issues in Elemental with spacing, returns and such.  Nonetheless, to each their own, and I trust myself more than I trust the .xml editor I have at this point.

And, to verify what BlackRainZ mentioned, some files need to be changed in the root directory, so if all else fails, try replacing the 'root file' after (again for emphasis) backing it up somewhere safe.

Mostly, I'm just emphasizing a lot of what has already been said.

Also, while you didn't mention the coremounts.xml file, the changes you are attempting aren't handled in that file as far as I'm aware.  For the benefit of other would be modders, mount bonuses and such are of course usually in the CoreMounts.xml, so that's a good place to start when tweaking bonuses that don't involve production rates.

Yeah, this makes modding the game really annoying and to make it worse you have to use Steam always in offline mode or your files are gone.

You can change the improvements from the mod directory, it's just a bit of a pain because you can't "edit" existing ones that way.  You have to block the existing ones (with an unattainable prereq) then create a new one (exactly the same as the sysem one but with a different name and  your changes included).

Better to do it that way in my opinion, a bit painful though for sure.

True, but what good does the online mode thing do for LH anyway?  I just turn it off.

If you edit the core files you could easily lose your changes that way too... if you forget to take a copy elsewhere.  If you get a patch, or steam checks you file cache it will overwrite your changes.