Many times a BGA rework technician will use a standard profile in order to remove the device, tweaking or adjusting the profile based on the results achieved. If there is the availability of a solder sample which allows the BGA technician to embed thermocouples into the solder balls (a corner, and 1 or 2 other places depending on the size of the package), into the die, around the BGA, near other components etc.
All in conjunction with learning about the thermal characteristics of the device and board during the reflow process. The proper method for embedding these thermocouples is high-temperature epoxy for their attachment to the device or internal to the PCB. Another “rule of thumb” for the reflow profile is making sure that for lead-free profiles the solder joint, as seen by the temperature in both corner and other balls, is above liquidus for a period of 60-90 seconds.