Yes you can shrink polyester in boiling water.
To shrink polyester in boiling water get the water to boiling and then take the polyester and get the polyester wet first and then while the polyester is still wet dip the polyester in the boiling water for a minute or so.
The way the boiling water shrinks the polyester is the boiling water breaks down the polyester fibers which causes the polyester to shrink.
When natural fibers and polyester is blended together the polyester can shrink much more and easier.
It can be hard to shrink polyester on accident but if you really want the polyester to shrink you can get the polyester to shrink.
I've used boiling water to shrink the polyester when needed and it worked great.