unfortunatelly there is no way to update tab controls line without tabPanel reRender. But if you will use switchMode = ajax then only current tab will be encoded on tabPanel reRendering.
Thanks for your reply Ilya.
If I set the swithType to "Ajax", i face the same problem even without adding/removing tabs. i.e. when i switch between two tabs where one of them has an iframe, the iframe source is requested again every time I switch to that tab.
So the only acceptable switchType is "Client" in our case.