to replace text in posts.
Code:
UPDATE post SET pagetext = REPLACE(pagetext,'www.olddomain.com','www.newdomain.com')
replace text in pms.
Code:
UPDATE pmtext SET message = REPLACE(message,'www.olddomain.com','www.newdomain.com')
to replace text in signatures.
Code:
UPDATE usertextfield SET signature = REPLACE(signature,'www.olddomain.com','www.newdomain.com')
you can acheive what you want from above queries