Changing headers in an Access Point

[David Shwatrz]

Hello,
  I am trying to understand how hostapd works. (when using the hostapd
daemon with some driver which supports operating in master mode).

My question is about data frames: as far as I understand, when data
frames are received in an Access Point, the packets should be relayed
for the final destination. Are any headers of this data packets
changed in the AP ? and in case this is so, is it done in the hostapd
code or in the kernel code?

Regards,
DavidS