You could always try this:
If you want ext 1234 ONS PLID 2-1-1-2 to actually be moved to ONS PLID 3-1-1-6 for example, create a temporary extension on 3-1-1-6 like 91234. So now you have 1234 on 2-1-1-2 and 91234 on 3-1-1-6. Go to maintenance and type the following command:
MOVE SWAP EXTENSION 1234 with 91234
Once the operation completes, 1234 will be on 3-1-1-6 and 91234 will reside on 2-1-1-2...simply delete 91234. Hope this helps.