Use multiple sprites for each part and build the bike out of them, that is the easiest and less time-consuming way. Some mods that do not come with the first/basic version of the bike, like say the lights, can be turned invisible by default when not bought. Then you have one of two options, you either use frames for each mod type (say for every type of light) and set the sprite animation speed to 0 so that you just pick the frame with the currently used mod.
Or you use separate animations if you want the mods to be animated, like banner flags or something. Then you just switch the animation of the "part" sprite to the one you need.