Alternate Labelling issue

Dear Friends,

My Structure Indicator is XX-XXXXX-XXXX

1 2 3

So previously my client created 4 characters in 2nd level.

Now if i change using alternate labelling in 2nd level, what will be the result in 3rd level.

Eg:

Previously : XX-PROD -XXXX

If i change PROD to PROD1 then wat will be the effect.

Regards

Mohan