Dear Harini,
Based on previous year's cut-offs it can be said that with your CMR 832 Rank you can't get preferred course B.Ftech, as you said you belong to General Category.
The previous year's cut-offs for B.Ftech course in NIFT Chennai are given below.
Category: General Category
2019 Closing Rank - 310
2018 Closing Rank - 332
But you have good chances of getting other courses like Textile Designing, Apparal Designing, Knitwear, Leather Designing etc as their cutoff is between 900 to 1800. I d on't think so you can change your caste at this point of time because you already got ranks. But you can try for it by contacting helpdesk team given in the official website.
For more information about NIFT cut-offs go through below mentioned link.
https://design.careers360.com/articles/nift-cutoff
Hope this helps.
All The Best!!
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