[BigPigeon]

I'm dipping my toes into 3DS Hacking for Fire Emblem Awakening, which has lead me to ctpktools, an application for unpacking and rebuilding 3DS image files. Unfortunately the github links on GBATemp are out of date. Does anyone have an active link they can share?

[Colmines92]

You can also search for "kuriimu" in github that serves the same purpose and personally it has worked wonders for me. The program has 3 executables, each with different uses, in this case you will need to unpack and repack 3DS ROMs would be "karameru.exe".
In case it is not what you are looking for you can also search in github "HackingToolkit3DS" of "Asia81".