Running cpp codes on Gazebo 9 written for previous versions of Gazebo

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Hi everyone! I am trying to catkin build a workspace from a git rep and procedure works fine with ros Kinetic but with Melodic I have several compiling errors. I believe this is because on Melodic I have Gazebo 9 while cpp codes have been written for previous versions. Do you know what I can do to fix the issue WITHOUT manually modify all the files in which there are some issues? Ex: cannot convert const boost to bool, or GetSimTime() is no recognized etc.. Thank you for your help