the presets will only effect settings that it needs to. It will not reset all settings back to defaults, or to whatever the preset settings are. Output resolution for example, will not be changed when using the exterior camera preset. Just make a backup or your options by saving them to a vropt file, or backup your whole scene. Then play around with the presets a little, and if you decide you would rather return to the settings you had, you can either load your backed up vropt, or you can load up your backup skp file.