Yes, you can decompile any unobfuscated .Net code i.e. with Red Gate Reflector. Unfortunetely the code was most likely optimized while compiling so the code will not be exactly the same. You will lose all comments also.
Converting to PNG would do the job, but you will end up having performance issues. Instead of using Texture.FromMemory() which requires the texture already being in a right format, you should try to lock the texture and fill it with the raw data. You could take a look at my Direct3D rendering implementation which is at Github.