These instructions will assume you have already downloaded and installed the version of the Highlights mod you want to edit.
To download the mod see this page
If you have a downloaded skin (or one you have created yourself) that you want to add the mod to there are two methods.
1. You can copy the panels and graphics folder of the Match Highlights skin into the folder of the other skin you are using and if prompted replace any existing files, then load FM turn the skin cache off and reload your skin and the mod should now be applied to your skin. (If you are using the FMC mod you only have a panels folder to copy over).
2. Change the parent skin of the Highlights mod to that of the skin you are using.
To do this for the Match Highlights Default Skin (Adaptive) you'd open the ibh_adaptive.xml file located in the ibh_adaptive folder in that file locate this line:
<flags id="parent" value="fm2013" />
And change it match the skin you want it to look like.
For example to get it to look like the Official Dark Skin we'd replace "fm2013" above with "fm dark-widgets" so the line now looks like this:
<flags id="parent" value="fm dark-widgets" />
The name of the skin you enter here is the name of the folder for the skin, which is located in your skins folder.