provided by: 
Reader Andrew Jacobs is interested in making big changes to contacts in Address Book. He writes:
Recently, a large company I do business with moved its headquarters and I'd like to change the address for all my contacts who work for this company. Is there a way in Leopard's Address Book to change multiple contacts at once?
Regrettably, Address Book doesn't include a bulk-edit feature, but there's a way to use Apple's TextEdit to solve this one. Try this:
Start by launching Address Book and choosing File -> Export -> Address Book Archive. This will create a backup of all your contacts. Should something go wrong, you can always return to this backup.
Now, create a group that includes the contacts who work for this company (use Address Book's Search field to help in this effort, select all the results, and then choose File -> New Group From Selection). Name the group, select it in the Group pane, select all the contacts in the group, and drag the contacts to the Desktop to create a single vCard (.vcf) file. (I suggest dragging the contacts to the Desktop rather than the Group because, at least in my testing, when you drag a group that contains contacts with embedded images to the Desktop, the resulting vCard file can't be edited with a text editor.)
Open this vCard file with Apple's TextEdit. Choose Edit -> Find, and in the resulting Find window enter the company's address in the Find field in this format: 123 Main Street;Anytown;CA;12345. (You can just copy the text from the file and paste it into the Find field.) In the Replace With field, enter the new address along these lines: 321 Broadway Avenue;Thistown;AK;54321. Click the Replace All button and close the Find window. The previous address should be replaced with the new address for all the contacts within the file. Save the file.
Drag the file you just saved onto Address Book's All group entry. A sheet will appear that asks if you're sure you want to import X number of cards. Below this question is an entry that reads "X cards are duplicates and will be updated." Click Import and the contacts you originally selected will have their information updated with the changes you made in TextEdit.
Read article at Macworld.com