[startv]

IR Power on commands are Hardcoded into U-Boot. As such Power On commands are only coded for the C1/C2 IR remote or Harmony remotes programmed as C1/C2 remotes.

This cannot be changed.

I suggest you use HDMI-CEC control instead to get your TV to power OFF / ON the C2.

Play with settings....
Kodi Settings > System > Input Devices > Peripherals > CEC Adapter > .....

I have a HTC M7 mobile phone with IR componet，I installed irplus APP in it。this APP can convert lirc file to irplus，So，I think if I have the
C1/C2 IR remote's lirc code, I can use my HTC mobile phone to power on C2 , am I right?

If you can capture the unique IR signal, then yes I suspect you can Power on the C2. That is what learning remotes do all the time anyway.

Lirc can be used to signal OFF but you need to learn the Infra Red - ON code from an existing C1/C2 remote. Or a programmed Harmony.

Who use irrecord to create a HK C2 remote's lircd.conf file, I think I can use this file and the irplus APP to power on C2.

I used the keycode 0x23dc4db2, but it didn't work.