Suggest you find the keymapping tool for your emulator and look at how the the keys are defined.
On every emulator i've used (more than 10) the newline key is "somewhere". Some mapping tries to use the original key placement (like a real 3270) as much as possible. Others to not try. Often the newline is the Enter or the right Ctrl-key. On a few systems it has neem SHift-Enter. Some, the easiest way to find the keys is to look at the keymap tool.
Mapping the keybroad will be a permanent change across all applications?
Unless the keymap is read from some network file (not usually done), individual desktops would need to be configured. If there is toi be a change to the mapping in general, new users would at least be properly configured when their systems were set up. Hopefully, there is already a newline mapped and all that will be necessary is to tell people how to use it.
IMHO - everyone using a 3270 to interface with the mainframe should use the same "standard" keymapping. . . If there are reasons to have "special" needs, fine, but the standard 40+ keys should be the same (for sanity's sake). Again, only imho.