First a caveat : There is always a chance when you do anything that the project will break. That's why we do backups / use source control.
Second, I am only a sample size of one, so this is hardly an official statement
However, I have been opening the same projects in both Windows and Mac IDE without any problems.
In the early beta versions of GMS 2, there were some compatibility issues, but I haven't noticed any over the past year or so.
Recommend you make a backup of your project and do some testing for yourself just to be sure.