This ones more formatting related than formula but I didn't know where else
to put it.

Say I enter the value c7454951000000cgvxx I want to pre-format it
with predefined '-' after a certain number of characters.....

I intend the formatting will change my value to;
C-745-4951-000-000-CGV-XX

I have tried the following custom format but it did not work..
#-###-####-###-###-###-##

Does anyone have any suggestions?

Bruce