To a huge extent, MATLAB code is forward compatible. Yes, there will always be changes that must be made. It is always true that TMW gives us advance warning that something is going to change. That warning will usually happen several years in advance.
In fact, I have code that is getting close to 30 years old that still runs with no problems.
If you want to know what has changed, then read the release notes!!!!!!!! These are notes that tell exactly what has changed with every release.
Yes, you can have two releases on the same computer. As long as you have a current license, you can have as many as you wish. I often have as many as 2-3, sometimes even as many as 5 older releases, though I do delete them periodically, since I tend never to use the old releases. I just don't delete the old release until I am comfortable that things are working properly. (In fact, I just checked, and must admit that I have the current release, as well as the past three releases on my computer. I do recall that Walter tends to keep those old releases and uses them to check when questions come up in an old release.)
