In more recent versions of MATLAB, if you drag a file from a folder into the editor window, that file will open immediately, even when code is running. I'm not sure since what release this has been the case, but I've known about it for a while.
It's a real shame that right clicking on a function name in the editor, and selecting "Open ..." doesn't work immediately when code is running also, but waits until the code has finished. It's much more of a pain to have to find the file in a file browser window. This seems like an easy thing to fix.