/s/1i5LMGML

Editing NCCH header
Open the NCCH header (might be ncchheader.bin), or CFA in your hex editor.
Find the unique ID in two locations:
0x109
0x119
Edit the two locations with your new unique ID.

Each unique ID is three bytes long and stored in little-endian, so the bytes are in reverse order. For example:
EDF is 000EDF normally,
00 0E DF when separated by bytes, and
DF 0E 00 in little-endian.