would muriatic acid take a fine layer of cement off aluminum without destroying aluminum?

Aluminum will be attacked by both acid and alkaline materials. There will be no way to stop the acid from also attacking the aluminum. How much it etches the aluminum will depend on the concentration and temperature of the acid.

I doubt it, unless by "destroy" you mean will it eat the entire aluminum part away, then it should be okay.

You may want to test it by putting a drop of muriatic on a hidden spot on the aluminum, but I suspect it will cause the aluminum to be oxidized, turning it from a slivery color to white.

Not likely. It reacts with metal faster than the cement. HCl is a very corrosive acid and it does dissolve most metals. Only 3 others will dissolve metal faster for the same concentration. I suspect that a pressure washer would work easier and safer.