Effects
You can apply a reverse-compression (a quick Google search will give you many results). This will make the sound more plucky and it will feel like a palm muted sound because the release length (ADSR) of the sample will have a lower volume compared to the other parts of the sample. Now you can apply a low-pass EQ and a little bit of distortion. Now layer this with the un-EQed original plucky sound. Adjust the mix untill you get what you want.
Plugin
You can use Guitar Rig by Native Instruments. You would easily be able to create the palm muted guitar effect by testing a few amps, EQing the guitar using the in-built EQ and adding a little bit of distortion. It is a very versatile plugin and if you are often dealing with guitars, this plugin will prove to be a boon for you.