genesis_tx

genesis_tx

curl 'http://api.forknote.net:8090/genesis_tx/' -H 'Origin: http://forknote.net' \
-H 'Accept-Encoding: gzip, deflate' -H 'Accept-Language: en-US,en;q=0.9,pt;q=0.8' \
-H 'User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/63.0.3239.132 Safari/537.36' \
-H 'Content-Type: application/x-www-form-urlencoded; charset=UTF-8' -H 'Accept: application/json, text/plain, */*' \
-H 'Referer: http://forknote.net/create/' -H 'Connection: keep-alive' \
--data '{"MoneySupply":"100000000000000000","EmissionSpeedFactor":21,"DifficultyTarget":60,"GenesisBlockReward":"1000000000","AddressPrefix":322560377,"Addresses":["imzt1vK1qVFNP5N4hMrgs96Fz4zvP9gJ5MTh1YpKVVVtBc54Co2K12J1sczeHe6DDQBsBkmfN37rxAWssaf7LU7eVmQWvRboxG31H"]}' \
--compressed

Source: https://monero.stackexchange.com/questions/2886/how-can-i-create-a-new-monero-genesis-block
Follow the above and change the unlock time bits to 3c is you unlock time is 60.
Go https://github.com/monero-project/monero/blob/master/src/cryptonote_config.h#L133 and screw around with the genesis tx and nonce. You probably also want to change other stuff (network id) to avoid contacting live Monero nodes.

I've helpfully decoded the genesis tx so you know/can guess what to change:

version
01
unlock time (varint, height, 60 here)
3c
vin length (value in)
01
vin #1 (of 1) type (gen, 0xff)
ff
height for gen input
00
vout length (value out)
01
output #1 (of 1) amount (17592186044415 as varint)
ffffffffffff03
output #1 type (to key, 0x02)
02
output #1 key (32 bytes)
9b2e4c0281c0b02e7c53291a94d1d0cbff8883f8024f5142ee494ffbbd088071
extra length in bytes (varint, here 33)
21
extra pubkey tag (0x01)
01
transaction pubkey (32 bytes)
7767aafcde9be00dcfd098715ebcf7f410daebc582fda69d24a28e9d0bc890d1