I view the forum from the mobile app, so seeing others locations is not as easy as from a PC.
I'm in the US, so I'm speaking from my experiences which may not apply to *.cn.
Yes it's still under warranty until you have a mishap that can be connected to your modification. If you modify, and fly safe, then unmodify later, the warranty would logically remain in force.
Using the phone example, if you flash your phone in the US, most manufacturers/carriers will say you're on your own unless you can restore the proper software and demonstrate the same defect.