I don't know if you mean the player character's head icon on the lives HUD ot the player character's head icon on the minimap, but I do know they aren't textures, so you can't open/view them in the texture editor. I'm having a similar problem with the camera buttons and the Power Meter, which are the same kind of files. IIRC, NSMBe could open that kind of files (I could be wrong here), but if you can do anything to edit them in SM64DSe, I don't know.

Kind of a bump, but I saw the OP lurked in this thread, so I'll post this information.

I was correct about being able to edit the 2D graphics in NSMBe. There is a tutorial on YouTube (by Shugabrush IIRC) on how to create custom icons for SM64DS. SM64DSe itself cannot open or edit these 2D graphics. Note that the logo is a whole nother story: it's in an overlay which you need to decompress, check Gota7's tutorial on custom title screens (misleading title; it's only about custom logos) on YouTube for that. But editing 2D graphics (like HUD/minimap ones) in NSMBe is a piece of cake!