Sorry, _ISO it is hard-coded into many of the scripts and menus, etc.. Also in the XML files used to install Windows, etc. It occurs in about 200 different files!
You could try a search and replace utility such as Find and Replace FNR.exe at https://findandreplace.codeplex.com/
You can replace every occurrence of _ISO with some other name but it won't be compatible with any future update, etc,
You can create additional menu folders under \_ISO\ and you can delete the existing menu folders (except the MAINMENU folder, and keep the WINDOWS folder if you want Windows 7/8 install ISOs).
Subject Re: Rearrange folder structure?