Override image dimensions set by image style
You could alter the width and height properties of your image(s) using CSS, it depends on the (base) theme you use in which file these CSS rules should be entered. However, the image produced by the image style is still used (so, this might not be quite mobile friendly).

Another option is to use the Image Style Selector (ISS) module, which provides an extra field on your node edit page that you can use to select an extra image style (to apply on the image on for instance your front page). When displaying the node on the front page you can hide the original image field and display the ISS field (the result is that your image will be shown using the style selected in the ISS field).