Hi Suresh,
If you dont lock the users,they will keep on creating the transactions and the LBWQ will be getting filled.
The structure has to be changed as per the new changes/enhancments ...has to be same as DEV/QA.
The Transports may fail and the new structure will not be overwritten,
In case you are sure the users are not login into the sytem (say midnight) then also you can do your transports.
rgds
SVU