Comparatively, the glans has a harder fascias (tissue layers) than the rest of the penile shaft as it's the first line of impact trauma and the ending point for the waste disposal. It may appears larger after pumping, but it's harder to keep it expanded permanently without a bit of harder work.
The good news about it is that the blood tends to be more concentrated at the terminal point than the rest of the penis, allowing more repairs and duplication efforts than the rest of the penis. To some degrees, it can be forced to grow faster, but based on clinical data, the permanent growth or expansion is slower overall.