Limiting the screen field to 30 characters is certainly a modification.
Without modification you can check the used characters in a user exit while saving, the error prevents the user from saving the material master until it is fixed. But his means he has no optical help to enter not more than 30 characters.
Must be a strange interface, most users already complain about the limit of 40, less will create a lot redundant descriptions and you would usually need classification as main way to search for items based on characteristics instead of description.