Numbering elements in Tekla Structures seems like irreversible operations but it can be reversed when you use this one option.
Use Save-numbering-save option
This causes saving the model before numbering then Tekla Structures show you the numbering dialog with all changed numbers allowing you to accept or cancel numbering operation.
To turn on this option you have to open Numbering Settings, check the Synchronize with master model (save-numbering-save) option and click apply. (I always save my numbering settings as standard to have the same numbering settings after Tekla Structures restart. I recommend you the same)
Numbering report window
When numbering report window shows the Tekla Structures freeze. You can read report and select parts in model by clicking on the report row. You can cancel numbering or save numbers.