Adding to a vinyl sculpt - advice please?

[cherry-blossom78]

I'd like to experiment with turning some of my kits into little monsters...adding horns, ears, fangs etc.

If anyone has tried this, I would really appreciate some advice...any tricks or tips for shaping the clay or helping to ensure it sticks?

And at what stage would you add the clay to the vinyl - right at the start or after the painting? Presumably fangs would be added after the lips have been painted? Ears right at the beginning to help ensure a paint-match?