When I read the FAQ, I think the difference between v2 and v3 is Internet Bridge.
If I change the v2 device's internet bridge to v3 bridge, will it change to v3 device? Will the device support Apple home kit?
Yes, the only hardware difference between V2 and V3 is the Internet Bridge, and the main difference is precisely the compatibility with HomeKit. If you replace the V2 Bridge with the V3 one, your heating setup will be compatible with HomeKit.