subsubsection format

[Nicolas Constans]

Hi,

I would like to know how can I change the format of subsubsection :
instead last number a letter, and text in italic.

I have :

1.1.2.3 Blabla

I want :

1.1.2.c Blabla

and Blabla in italic.

I suppose it may be possible with the use of so-called "ERT" but I
don't know how.

Thank you very much in advance,

        Nicolas.