Hi,
this is not possible to rename nodes without removing it and creating it again with the expected name.
With 2000 nodes, it may be long to browse node list and that's why you enter again the node IP address instead of selecting it in previously created nodes...
with such a long list of nodes, you may manage your F5 with partition to create pools, nodes and virtual servers classified by projects and not listing other projects nodes and pools.
To rename all nodes, you may try to list all nodes with command:
list ltm nodes one-line
Then, create for each node the delete and the create commands:
For the node testnode IP 1.2.3.4, :
delete ltm node testnode
create ltm node 1.2.3.4 { address 1.2.3.4 }
Execute it in transaction:
create cli transaction
delete ltm node testnode
create ltm node 1.2.3.4 { address 1.2.3.4 }
submit cli transaction
it will execute both commands and will submit it only if both finished successfully.