There is a plugin to open .dds files in Photoshop, just google it (should be on an nvidia page cause it's a Texture file to work with Nvidia stuff)
RomFS\bin\appli\live_comm\bin\live_comm_top_00.arc
Images are probably stored in this file.
I tried to edit one, but the game crach after the press start screen.
It bother me, so I stop here, if anyone want give a try, go for it.
But there are weird issues when replacing them (game can crash and stuff, like on the 3DS)