I would start with an export of the current configuration, and based on the format of that file create a new import file with the customer's list converted to that format.
You may want to write a script of some sort to do so.
In general, in my opinion, it is also wise to normalize the input. Often adjacent sub-ranges are written on separate lines.
can be rewritten as
But that is a matter of choice/policy.
There are there different ways to create to handle this kind of request.
Please check the following link for better understanding.