Cannot be done. There really is no such thing as renaming an Item. To rename an Item what actually happens is the old Item is deleted and the a new Item is created with the new name. Since it’s a new Item you won’t be able to expose it to IFTTT through the Cloud Service. You are stuck with the old Item names.
If it’s really a problem you can use a Proxy Item and Rule to translate events from the IFTTT Items to your renamed Item. But you won’t be able to change the name of the Item and have it still work with IFTTT.
Other alternatives include:
Host your own openHAB Cloud Server instance, turn the Item exposure feature back on and link that to IFTTT
Use the web service calling IFTTT Channel to send commands/updates to openHAB and/or the webservice receiving IFTTT Channel (or what ever they call it now) to send stuff from openHAB to IFTTT. You’ll need to use the HTTP binding for that part.