(NES) Add sprites to screen

[Mr. Saturn]

So I'm working on a hack for Super Mario Bros. 2, currently changing the characters. I recently learned that the white pixels that make up the characters' eyes are actually separate sprites behind the characters.

I found where the sprites are located, but their placement doesn't fit my new sprites.
I need two sprites side by side, covering the entire head, rather than just the front half of it (I found that SMB2 uses 8x16 sprites if that's helpful). This applies to every character, so using up their eyeball sprites for this would be fine.
Another problem is that Toad also needs eyes, but one thing at a time I guess.

If this doesn't work I guess I could find some way to change the palettes of each character's heads (and this would let Toad also have proper eyes), but I don't know how doable any of this is.

I found SMB2's disassembly code which seems helpful, but since I'm still figuring that out, so I thought I may as well ask here.