I would advise against repurposing AAMs to SAMs. The inherent design advantage that SAMs possess is that they don't need to be as light and compact as possible. You can free up those parameters because you're launching them from the ground, where space and weight isn't an issue. This makes their development and procurement cheaper, and you tend to need a lot of them to cover saturation attacks. Rippling hundreds of PL-15s is gonna cost a fortune, especially since most of those shots would be against decoys. Also, a SAM's larger dimension increases the available space for the seeker and ECCM components, which can be larger and more powerful, while being cheaper at the same time since they don't require the same level of miniaturization.