CNC QUERY on exiting a holding

I bought some shares of TCS on CNC and after it was in my holdings I sold it at a profit. After selling, the stock had gone down & it was showing in my positions as a profit of Rs.2500 odd. In such a situation can I again exit (buy) and pocket this profit?

Yes you can, this will be considered as Intraday trade.

There is also an option to convert to MIS. What is the difference between the two?

This option lets you convert your CNC position to MIS. Only difference is you require less margin when you use MIS and your position needs to be squared-off before 3:20 PM or it will be squared-off by RMS (you will be charged Rs. 50 + GST for this).

Is this trade possible the next day(T+1) also?

Doing Intraday trading with Stocks in your Holdings? Yes it is possible.