Modifiers can be used directly in Slic3r in order to assign different print infills to a same file. Unfortunately, this feature is not available directly in HeartWare, so you would need to find the Slic3r program (which should have installed with HeartWare) and open it.
In order to change an object using this method, you would need to create a different object (.STL) with the measurements (usually big enough to cover the X and Y areas, and the height you would like for it to modify), and import it into Slic3r. You can follow these steps:
1) Open Slic3r and import the desired file. The program will probably be located under “C:\Program Files\Repetier-Host\Slic3r”.
2) You will need to create a modifier STL. To do this you can use your preferred CAD program and generate a box (or shape that resembles the most to the type of modification you would like to do), with the desired measurements of the modification. i.e. if you would like to print a different infill pattern for the first half of the file, you would create a box that occupies the entire object in the X and Y axis, and only half of the Z axis.
3) After having imported the STL file that you would like to print. You will need to add the modifier STL by right-clicking on the object, and the clicking on settings.
4) You will then click on “Load modifier”, as seen below. This will prompt you to select your modifier files. You can select multiple modifiers for different parts of the object.
5) After you have selected the modifier files, you can select which type of modification you would like the file to perform. E.g. infill density/pattern, print speed, etc.