NMF and Future

As Gerald said, clear coating any NMF will alter the appearance.  With Alclad polished Aluminum, you should be able to decal without a gloss coat.  Alclad is a lacquer, so you can use an acrylic wash to define panel line detail without a topcoat.  There are some risks involved however, so the advice to try first on a scrap piece is good advice.

Regards,  Rick

Anytime you overcoat with a clear coat you change the look. If you applied a matte sheen aluminum, it will now take on a glossier look. I would spray an old fuel tank and see what you think, is it acceptable to you or not. Then decide whether or not you will apply it to your project.