As long as you have appropriate expectations, you can get this done with rattle can. It's a job that does reward additional work. The more sanding and preparation you do, the better it will look. But if you just want to slap some paint on and ride the thing, you can do that too.

I have a Raleigh Competition that I had bottle cage bosses and mid fork braze-ons added to. I wanted to keep as much of the original black paint as I could, so I sprayed the modified bits with Rust-Oleum Gloss Black Enamel (after proper priming).

Here it is before my paint attempt:



Here it is about a year and a half later:



Most of the time when I see a spot on the bike that looks bad it turns out to be either the original paint or an aging original decal.