I own DJI F450, P3A, P4PRO+, and Spark. I like the P3A, Phantom 3 Advanced, most.

However, its camera is already a bit outdated in comparison with P4Pro and even Spark. Is there any way to change the camera on the P3A?

I have got 3 batteries for P3A, which still provide 20+ minutes of flying time, the DJI P3 backpack. Its range and reliaibility are simply great. If I had a new camera on it, I could still use it for years.

Your only option is to use the camera from a P3 pro which is a simple job to fit.
You have to then update firmware with P3 pro firmware because your drone will now be a P3 pro.
The only additional feature you would gain is 4K video rather than the 2.7K video you already have, so it's not much gain for the extra $$ spent.