In practice this is not effective, for as someone else noted, tracking can and is done at server level as well.

Most implementations, though, make the assumption that if they get JS info, that info is good. Better to give them wrong/inaccurate/changing JS info than no info.

So, I leave JS on, use some personal plugins to change variables and give them bad data on each request. They won't know and will just get bad fingerprints that are not seen again.

See this comment: https://news.ycombinator.com/item?id=6046810

Would it be possible have the source of those plugins open?

User-agent, ip, country of origin etc can be obtained server-side by reading web server logs. What you can do is change your user-agent manually, use different proxies to get another IP etc. tl;dr: do a lot work that will make you waste time and bandwidth (proxies are slow and/or costly).