[oem4me]

I've had some luck shooting touch ups and blending in over the original paint (it's enamel, not lacquer) by using "metal prep" and a scothbrite or fine steel wool to clean up light rust and de-gloss the orig paint surface. I cannot recommend this as a long lasting, professional approach, but I personally have not had any failures even after 20 plus years of indifferent care.
I think most would argue for a sealer between new and old paint, but I'm here to say I've cut corners and gotten away without it.
You'd be smart to test first way down low or on a spare part or something.