Could SIkuli change some environment variables at runtine?

Not a feature.

You have to do that in some wrapper (command script, ...).

Or in your SikuliX script/program using the JNA features (JNA 5.3.1 is bundled with SukuliX already).

An example for manipulating the Windows path you can find in the sources:
class: org.sikuli.script.support.RunTime::addToWindowsSystemPath

Ok thanks.
But while executing a normal script it does not change anything related to that, right?

--- But while executing a normal script it does not change anything related to that, right?
not while running, but before starting the script run, the lib path is added to the end of the Windows path.
But this does not clash with any wrapper actions.

Sorry, my bad. I was not clear enough.

To be more specific, the problem is:

We are testing an app(MyTestApp let's call it) and we have a large suite of tests built with sikulix+python. This are executed on two virtual machines from TFS.

'MyTestApp' uses a module called 'pdftk' when you open a pdf doc from this app. The app is adding at installation to windows Path this : C:\Program Files (x86)\PDFtk\bin, in order for this module to work.

On the VM when sikuli script is trying to open a PDF file the path to PDFTK is not found anymore.
It works locally, no problem.

I know it should not have any impact no matter how many things you have in windows PATH, but could it possibly be something from sikuli like changing something in path variable or something similar that could affect other paths already present there?

ok, you can do that in a script:

try:
  import org.sikuli.natives.WinUtil as Windows
  path = Windows.getEnv("PATH") # get current path
  # manipulate the path string
  newPath = Windows.setEnv("PATH", changedPath) # change it
  if (newPathh == changedPath):
     pass #worked
except:
  pass # did not work