I am writing an alert script in Python 3, and I'm wondering if putting the second python interpreter on my Windows box will cause problems with the Splunk installation. My Splunk admin is hesitant about mixing the two, but I believe if I keep the new version out of the environment variables I should be able to call it from within my alert script with #!/path/to/paython3 without disturbing Splunk's normal operations.
You are correct. You can install the other Python instance elsewhere, and explicitly call it. I'm not sure Windows respects #! at the top of script, in fact I think it doesn't, so you'd have to code the path in the appropriate place.