I need to use a watch dog for the mega because i am loosing connection with ethernet shield in random times...
but it seems that the wacth dog dont work with the MEGA2560 , to fix this the only way is change the bootloader to this
or is there any other workaround?
You seem to have identified the problem and the solution. I'm not aware of any alternative solutions, but I don't see any reason not to use the solution you already know of.
Intermittent Ethernet connectivity problems don't strike me as a good reason to reset the Arduino, by the way.
Just a feedback.
i am using this method , and 99,9% of the problems solved with watchdog,,