asokol,
I assume your codes are in the following format:
LLDDLDDDDDDDL,
i.e. fixed length and the letters (L) are always in the same position,
then, if the first code is in, say A1, the following formula will
generate the next element in the sequence:
=left(A1, 9) & mid(A1, 10, 3)+1 & right(A1,1)

HTH
Kostis Vezerides