Manually updating config files on a mac

Hi,

I'm updating my FM stadium pictures to add new stadiums and am manually updating the config files for the new pics.
Every time I open the config file to edit it, it changes the file somehow so that it is no longer compatible with FM.

I am using a mac rather than PC. It was a lot easier previously on a pc.

Does anyhow know how to open and save the config.xml file on a mac so that it is still readable to FM?