How do I get hardened glue off celluloid?

[Shaun_of_the_red]

Yeah so I glued some cracks in the plastic shell of my accordion back together, clamped them, and let them sit overnight. I tried to wipe away as much of the glue as possible when I first clamped them, but couldn’t avoid some smearage. I’ve been warned against using acetone but alcohol isn’t doing anything—well, it is making me care less the more I drink it—but it’s not removing the glue stains. Help please! I want these repairs to be as invisible as possible!

 

[colinm]

Rub it down with a polishing kit and finish off with the finest compound.

 

[Dingo40]

I want these repairs to be as invisible as possible!

As colinm said (above), once it's hardened, polish it out using ever finer cutting compound.
Like duco (which originally was also made of nitrocellulose, similar to celluloid) repairs to a motor car.