Usually false. In most states, you do not have to use a specific form. About 37 state statutes include forms for appointing proxies or for creating comprehensive advance directives. In the majority of these, the forms are optional. In about 18 states, the forms must be "substantially followed" or certain information disclosure language must be included in the form. Even with these requirements, changes and additions to standard language are permissible. Indeed, any form can and should be personalized to reflect the individual's particular values, priorities, and wishes. If you do not agree with language contained in an approved form, change the language.
If changing the language creates any doubt about the validity of the form, then further legal consultation is in order. Above all, it is a mistake to pick up an "official" form and just sign it unchanged, without first being sure that it truly reflects one's specific wishes.