Can I modify lightmap by hand?

I'm making a scene for mobile using the T4M plugin, and it only support 4 textures. I want to have more textures. So, I split the mesh. Then each mesh will have 4 textures to use. But, the side effect is the crossing area will have heavy ao effect...

I want to erase this ao effect.

I've heard that the lightmap can be modified by hand (maybe in photoshop with some plugin? ). Is it possible?


the light maps are simple .EXR files.
so any image editing software that supports the format should do the trick.