10.4 SYSNAND Any way to install homebrew and mod?

I have 2 3DS's. BOTH have 10.4 One is a mario 3DS / the 2nd is a NEW 3DS.

I'm experienced in modding Wii. This is my first crack at a 3DS (no oun intended). Am I correct in my assumption that a 10.4 SYSNAND cannot be downgraded and modded? From what I've been reading that requires a hard mod / reflash?

Thanks!