Replacing the contents of one field with a group of selected records all at once -( without harming the rest of the database / records)

I have about 1000 records within my database -- I'd like to change 1 field within 50 of the records. Is there a down and dirty method of populating the one field within all 50 records at one time? The query to obtain the 50 records is pretty straight forward. if the word APPLE were contained within the field for all 50 of the records, how do I change the word to BANANA without harming any of the other records??? I export my database as a kind of 'security' measure, but would hate to try to bring it all back. This email message and all attachements transmitted herewith are trade secret and/or confidential informtion intended only for the viewing and use of addressee. If the reader of this message is not the intended recipient, you are hereby notified that any review, use, communication, dissemination, distribution or copying of this communication is prohibited. If you have received this communication is error, please notify the sender immediately by telephone or electronic mail, and delete this message and all copies and backups thereof. Thank you for your cooperation.