RegEx Validation for Custom field

Is it possible to perform regex validation on a custom field when entries are added?

I have a custom field that stores comma separated values that represent BISAC codes. I would like to run a regex against them to ensure that they match the convention of three alpha characters followed by 6 digits.

I have the regex, but is there a way to apply this to values in a custom field?

I looked at the search_template fields, but it feels like validation and search function should be different.

Failing this, I can implement it as a search or a plugin if I need to.

Thanks

Joe