the contact table

Here in .fo we want to use a few fields in our database table, which are not existing in the Fred Postgresql database table "contact". At the other hand there are some fields in "contact", which we dont use, for example "vat", "street3" etc. Because we want to make our system as much as possible within FRED (and as little as possible with database tables outside of Fred), i would like to use for example the fields "vat" and "street3" for other purposes (with other data). Can you think of any problems, i might get later because of this, or should this be an ok solution ? Are these fields hardcoded anywhere or for any purposes, for example in the Whois program ? regards Peter