Hi Shailesh,
From my point of view, the best solution for your issue is create a derivation rule, so all the documents created in the system before the date of the go live must use and specific commitment item, fund center, etc.
If you want all those documents with imputation to the budget, you have to use the standar SAP programs for this requirement.
Of course your solution (desactivated/activate) is going to work, but is no good practice, for example if someone post a document during the desactivation, you are going to have problems in the future
Regards
GVR