Customizing WBS Code?

[hugh jass]

Hi there,
Wondering if it is possible to customize the WBS to use numbers defined by
me or even letters.

For example, if responding to an examination that lists questions from E to
H,
I would like to respond in the same format:
E
E.1
E.2
E.2.1
E.2.2
E.3
etc...

For one reason or another, I may need to skip a number or start at a number
other than 1:
3
3.1
3.2
4
4.4
4.5
7

Is this all possible??
If so, how does one do it?
Thanks a million!
hj