I've had my fair share in rom development a year or so ago. And I can tell you that the name there is just a way of marking the rom.
But if you're really bothered by it, I can tell you how to find the string, edit it or completely remove it. To find the string - Custom build by Rocky, you can't just change it in build.prop. For this, you must go into /system/app and then copy Settings.apk file to your desktop. From there, go ahead and decompile Settings.apk with a preferred decompiler. When decompiled, head into the project, and navigate to the following folder - res/values and open strings.xml with a text editor. Search for Custom build by Rocky in the text file, once found. You may change it to whatever you wish. But if you want to remove it, you have to remember the ID of the string. For example, in - example text - which is the string, the text to the right. The ID is text the ID is found in the left hand side, it's after the word name . So remember that, now go back to the res directory and scroll down to the xml folder, open it and look for about.xml. In there search for text which is the ID. And remove the line completely. Also make sure to remove the header line too. As this will stop the layout from having an invisible section.
Now compile the Settings.apk and push it to your device - adb push desktop/path/to/Settings.apk /system/app or just copy Settings.apk to device and do it from there.
I do not encourage you to do this. And you can do this at your own risk. I will not take any responsibility if you mess up your phone.
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