Is it safe to use ROWID to locate a row doing update?

If the strings length changes a lot, the rowid could change.

it will be safer to do it with PK together:

update t
  set...
where rowid = :x and primary_key = :pk;

Reference:
http://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:53140678334596