ikhsaint, decrypt it, then edit it:
make_npdata -d encrypted.cpk decrypted.cpk 1
After editing, back encrypt it to SDAT format:
make_npdata -e decrypted.cpk encrypted.cpk 0 1 3 0 16
encripted.cpk - must have only the original name, because the hash of this name is written to the file during the encryption.