GreenCard holder looking to study abroad.

Hello there.

I'm looking to spend 1+ years studying abroad in Japan. I'm a GreenCard holder of 15+ years, and I'm actually in the process of naturalization and waiting for the oath ceremony. The thing is, the school term starts in October, and I have no way of knowing when I'll be called for the oath ceremony.

Naturalization aside, my question is:

Can I leverage a re-entry permit to stay outside of America for that long of a time period without losing my GreenCard?

Thanks a lot.