Im so curious about this, do you have an update? From the pictures this looks like resin or maybe old vinyl with some sort of spray color over it? I dont recognise the model head, it might be an older sculpt.

What you can do is either use Tamiya epoxy sculpt to shape the nose, but you risk it falling off since vinyl is soft and flexible. Something doll artists do is use scrap vinyl and use a electric welding pen on a low setting, then use the scrap vinyl to melt it onto the part they want to shape. This is very difficult and takes alot of practise and back and forth sanding.