It seems you are dealing with DS SDK graphics formats, however here the game uses a slight twist and sticks the ncgr (the actual graphics part of this) in .pk files. This might confuse tinke a bit as it will not want to load the related NCER (the parts that tell the tiles how to arrange) or NCLR (the colour palette). You can extract them out of it, stick them and the related files into another DS ROM, edit there and then export it all to import back into this if you want -- it is a bit of a cowboy method but I use it often enough when archives and name issues happen that confuse tools like tinke and crystaltile2.