If your work does not allow a nose piercing, why are you risking losing your job over a teensy dot of metal?
That's the worse case scenario. The second worse one is that you wear really tiny jewlery and they make you take out the piercing, at which point you will most likely have shelled out about $50, and all you'll get for it is a tiny healed dimple on your nose. I'm not sure what the point of that would be. (and yes, many nose piercings do leave some sort of dent/mark on your nose for the rest of your life even if you take it out)
You cannot wear a nylon or acrylic nose retainer for healing a piercing as the material is inappropriate for raw piercings and can cause increased adverse reactions, which really wouldn't help hide it.
And nose piercings take about three months to heal.... Are the co-workers at your office, and your boss, really going to feel ok if you wear a mask for three months?
I've never known anyone who worked at a place that forbid face piercings who was able to get and heal one without either leaving their job or being made to abandon the piercing.