as a note to self... in order to find it laters...

This will only alter the value of fieldname if the conditions in the WHERE clause are met. With replace we only replace a certain string within fieldname with the replace_with string

UPDATE `table` SET `table`.`fieldname` = replace(`fieldname`, 'search_value', 'replace_with') 
WHERE `table`.`firstcondition_field` = 'firstcondition_value'
AND `table`.`secondcondition_field` = 'secondcondition_value'
AND so on...