Hi Aravind,
Its always the best way to actually go and update the org values in the roles manually rather than manipulating the tables directly.
In my earlier projects, I have tried to use LSMW scripts in the foreground using recordings with marginal success. Its needs to be done with utmost care, else your rework might end up taking up more time and effort than what was required originally to do the work manually one by one.
Since its a one time activity, I would still recommend the traditional approach, rather than the time and effort saving automated approach. In the end, patience always pays. 
Thanks,
Rajesh