Conversion epub-->azw3 with negative margins

I am looking for an option to convert my epub collection to azw3 and I would like to get negative margins for my kindle paperwhite 1.

I do this now manually and I change the css to this :

p {
margin-left: -40px;
margin-right: -40px;
margin-top: 0;
margin-bottom: 0;
text-indent: 1.2em
}

The margin-left and margin-right to -40px. I am looking for a way to do this when I convert the books to azw3 without having to change the css files manually.

The problems I get is that not all the css files are the same. Sometimes people use the p option and somtimes the div options or they put the margins in the body.

Is there a way to get this right while converting without doing anything manually?