Adding a new index MAY change the CRC of the table. It may not!
The programs that should need the new index will need to be recompiled to make them aware of it - they will continue to run with the old indices until the recompile is complete.
It is probably worth recompiling every program that references that table, since it may result in changes to multi-index resolution which may or may not be advantageous. I would certainly recommend it if you can.