Can an Author modify his study post published ?

I had read that study about cold shower on 500 worker 6 months ago, i remembered clear improvement with CS for 30/45/60s post hotshower.

Something like 40% decreases in flu, stress score going from 1-4 to 0-3 and so on.

I got back to the study and.. thete seem to haveabsolutly no improvement in any area with cold shower.
My memory is alright guys, when i love something i remember. I may also save these score has screenshoot so gonna go search this in my collection (1000+).

Btw the study : https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5025014/#!po=33.8889