Programming :: How To Parse And Modify Keywords Using Shell Script?

There is a file with that format of each models' information.I don't think that's good format, but I cannot change that format. I needed to modify the model name, 'model = xxx' as 'model = abc'.And I don't know how to parse and modify 'model = iii' and 'model = ddd'.The only clue to parse 'model = ddd' is the second 'model = ' after the second 'system information'. But how to parse the second keyword?Is it possible with 'sed'?I sometimes have to modify the information of the file.using shell script if possible.Python is ok. (Shell script is better for me.)