Thanks for your help, this is starting to make sense now.
The integrating extensions wiki is what I needed after all, except as you say, I install the extensions to a different folder so they are not loaded automatically on boot.
Have built my first remastered iso but made the mistake of installing brassero to burn it --- I think brassero must have about 200 repository dependencies!!!
Still dowloading ... hope I don't run out of memory.
Thanks Again.