I have tried to open journal files directly with JMP but i cant set it as a default file type in Settings. When I try to Open With, it only shows 'Just Once' option and doesnt let me select always open as. JMP is not there in my default programs, although .jmp and .jrp are set to open with JMP.
If you cannot do it by right clicking on the file (I'm using Windows10 : Choose another App -> More Apps -> Look for another app on this PC)
You could try resetting file associations Problem Note 52261: New instance of JMP® is opened each time a new file is opene... - JMP User Commu...