Ubuntu will use grub2 and replace grub, unless you choose to write grub to
another drive or partition. You can do that by clicking the Advanced button
on the last page of the Ubuntu installation (it used to be page 7). This is
the page where the choices are reviewed after you provide your user name and
password. My experience is that Ubuntu's grub is very complete and will
detect any installed OS and I have at least seven installed on my computer
at any given time. Ubuntu is one of the best IMO at setting up grub. I have
three drives and three grubs but I only use Ubuntu's because it just works.
I can boot other grubs by pressing ESC and running the boot manager that
comes with HP and ASUS computers.
No, it is not difficult to edit grub2. It is much the same as grub legacy.
The file is called grub.cfg instead of menu.lst, but it looks much the same.
The mechanics are a little different, but after looking at the grub.cfg you
can figure out how it works.