Replacing Maxis Cells

[ProfAlba]

Hi,

So I've been remaking all the cells from the cell stage and would like to replace all the npc and starter cells.

I've found this tutorial but it's incomplete as there no way to modify starter cells with it and I would like to know how to make it from scratch since all the pngs are custom cells and I have no idea which one is which.

I would like to know what package file maxis creations are in so that I can replace all the starter and npc cells. I think it might be the pollination file but haven't managed to get anything functional out of it.