You have 10 characters at your disposal.
That means you have billions of possible combinations for the bin address.
So, the question is how much do you really need this extending of this field.
Because, I think that it's not wise playing around with these fields.
This filed is used in so many programs, and although it is most certainly referenced with a statement "LIKE LAGP-LGPLA" (meaning it will be a data type of LAGP-LGPLA) there are certainly other limitations where this extending would break standard code.
But the answer is yes, you can extend it, get help from BC consultant, but I have to warn you, the repercussions can be huge.
So, again, you have billions of combinations and I'm sure you can find a solution to narrow your bin number to 10 instead of 14...
Regards,
Mihailo