Robin, that would be a good idea for the doors to paint the red first. The hood is more of a challenge. The decals I have are from an earlier version. I want to replicate the paint scheme in the picture you provided. The earlier version has the lizard head and the heart outline only. I will need to paint the red to the edge of the hood. There is a line of silver that separates the heart shape from the red to the edge of the hood. I was thinking decal, seal, mask, seal the edge of the masking then paint the outer edge of the hood red. The decal will have to be masked somehow. The earlier decals are correct in size and shape, they just changed the location of red on the car slightly and added more red to the hood.
Let me see if I got this right:
1. There is a decal on the hood
2. The edges of the hood are red
3. Between the decal and the red there is a narrow strip of silver.
That would mean that you will need to copy the outline of the decal to make something that overlaps the decal by the width of the silver strip. This mask will have to protect the decal without lifting it or other wise ruining it.
I would suggest doing this by copying the shape of the decal onto paper. Adding the required width of the silver lining. Cut out the mask. Paint the hood solver. Attach the mask to cover the silver and paint the red.
Since you would be using paper you can simply start cutting another mask if the first attempt isn't perfect.
When the mask is removed there is a large patch of silver surrounded by red. Now it is time to attach the decal to the hood.
There is double sided adhesive tape, Scotch 136D for instance, but there are probably others as well. https://www.amazon.com/Scotch-Double-Permanent-Handheld-Dispenser/dp/B01J7SM58U
Stick this to the underside of the mask and cut to shape.
After some handling the remaining sticky side will be less tacky
You could also cut the mask exactly to the size of the decal and use masking tape to tape it down AND add the extra size for the silver lining.
In theory you could also make a reverse mask to cover the red while painting the silver but this would become very difficult to handle. Maybe by making the mask by taping the shape with narrow masking tape.
A clear coat over the silver before attaching the mask could be a good idea. Spraying the edges of the mask with silver before the red helps prevent the red from leaking in under the mask.
There is also a product called Parafilm which I know some modelers use for masking on aircraft, I have never tried it ...https://en.wikipedia.org/wiki/Parafilm