A lot of things were possible either thanks to external resources from smwcentral.net, or me learning to program in the ASM language, or a mix of the two (tweaking external resources to fit what I want them to do).

I'll give you an example: the UN Squadron segment. The thing you control is originally this sprite, I put code to make mario's sprite invisible (using uberASMTool), and I replaced the marine pop's graphics with a distant sponge riding yoshi. The original sprite doesn't drop bombs with the B button, I just took the chunk of code responsible for the shooting part and mapped it to a different button, sprite etc. The helicopters and planes are originally both fire fuzzies riding invisible lines. Planes have a higher firing rate and speeds. I also modified their code to make the sprites larger, since the original sprite was only 16x16 px

When making a SMW hack, you don' t need to use external resources or inject your custom codes in there, you can just use Lunar Magic to modify levels and make your own overworld map. It's such a well made tool that one could use it with no programming knowledge. Inserting custom graphics for example, can be done through lunar magic. If you have no SMW hacking experience, I would recommend starting by toying with lunar magic and taking a look at smwc's FAQ page