If you want to create a new validator, it is really simple:
1. create a new rule in :
models/rules/iban.php
Copy paste another rule to give you the example (you can copy email.php it is the easiest)
2. Rename the class, and rename the fork caller (footer of the file)
Note that if you directly create the rule in the fork folder (fork/models/rule/), then I am not sure if it works. Must check that.
Anyway, if you don't create your file in the fork directory (as I tell you), then be carefull when you upgrade your component with fresh generated. That's the only point.
If you encounter problems with that, please up the topic.
3. The regex
in the regex property, write your regex as it appears in JS.
4. In the form set your new "iban" validation
The validator itself is ugly and I would like to change it as an choice option.
If you know nice validator to integrate, I would be amazing. (I did'nt checked news about that for long time)