You should try to only write code in the designated areas that are usually marked by a comment containing something like this:

// USE /[MANUAL GEN CONTROLLER_NAVIGATION ARRBD]/

After you have tested the code and before you generate again you will need to copy that code into the body of a manual code entry in you project definitions inserting it into the list in: Definitions -> Manual code -> Manwins. Paste the code you wish to retain in the body of the manual code entry.

You can use the comment as a guideline to parametrize the manual code entry. In the example above the manwin type would be CONTROLLER_NAVIGATION and the parameter would be ARRBD. After this you can generate the code again and the code you added will end up placed at the comment shown above.

Note that some code will be added below the comment, some code may replace the comment and some code may be surrounded by additional code like try catch blocks or function headers.