Do take the benefit of booking from Mysore to Chennai as confirmed tickets are available. But remember ..... one thing ...... to keep the boarding station Mysore only at the time of booking the ticket.
After ticket is booked, go to any PRS booking office and meet PRS Chief supervisor with counter ticket or print out of e-ticket and give an application for change in boarding station from Mysore to Bangalore which he will do by way of endoresement on your ticket. So officially you will be allowed to board the train at Bangalore and no worry of your seat, it will not be alloted to another passenger. In this case, TTE will be allot the seat to...
more... any other passenger for the route between Mysore and Bangalore. At Bangalore, it will be vacant for you to occupy. Such change in boarding is free of cost. However the time limit for such change in boarding point is 24 hrs before the departure time from the original boarding station i.e. Departure time of train @ Mysore.