I often do the 'BMF before painting' procedure for chrome badges. Of course it has a lot to do with the quality of the engraved scripts or badges on the body. If the scripts are well molded on the body, the result is much better than PE scripts.
Before any work is done on the body, I tape over the script or badge with a small piece of masking tape just large enough to cover the script. This protects it from damage during the priming and body prep stages, preserving maximum crispness of the molded script.
After the prep work is done I remove the masking tape and replace it with a piece of BMF. Burnish it carefully into the contours of the script or badge. Give the area one last (light) shot of primer, then feather out any visible BMF edges.
Paint body as usual and let cure. The trickiest bit is removing the paint from the script without messing up the BMF. I use a number of tools for doing this; fine Micromesh abrasive pads, pencil eraser sometimes dampened (not soaked) in lacquer and sometimes without, toothpick dipped in thinner, eraser with fine polishing compound, etc. The two primary tips here are; use lots of magnification, and work very slowly & carefully. Don't rush it. The result can be stunning. For some scripts, following up with a touch of black washing adds much realism.
Definately try this on a scrap body first. With a bit of practice it can produce spectacular results.