Existing home loan borrowers must move to external benchmark loans

Yes, there will be some cost, but it will be limited to administrative and legal expenses

Existing home loan borrowers and micro, small, and medium-scale enterprises have a new option — loans linked to an external benchmark.
 
The Reserve Bank of India (RBI) mandated in October that all new floating rate loans will be linked to an external benchmark — this is the new normal for loan seekers.
 
With the State Bank of India announcing a 25-basis point cut in the external benchmark from January 1, borrowers linked to this would reap the benefits soon.
 
Old borrowers can explore this option because calculations are much more transparent than the benchmarks that they are