Hey! Glad you are wanting to get your feet wet with mods! Right now, the thpsGoat site is working on adding a tutorial section for these types of things along with tools that will help you accomplish what you want. In the mean time, you could look for the TGA2IMG tool yourself maybe over at thmods. You would need to create a TGA texture that has an alpha channel. What you would then do is simply save the image as a TGA and run it in the TGA2IMG tool to get your image to the img format. Then you would simply replace whatever shirt logo you desire! (Video tutorial coming soon at my website as mentioned above)
