Modify plugin without it updating.

I’ve found a plugin that does mostly what I need but I just want to edit the code so that I can have the extra functionality that my client wants. I’m worried though, that when the original author updates their plugin in the repository that my client will hit the update button and lose the customised version.

Is there a way I can change the plugin so that I still give credit to the original author but stop it from upgrading. Is it as easy as changing the name of the plugin in the php code and the version information in the comment code?