Hi. I don't think that you can change your category. It will already show you your caste while you will fill the form for cap round. Even though it gives you the right to fill your caste again but your seat might get cancelled because of the different caste. So its better if you just go with the same caste which you filled in your MHCET form. You should try to talk to the concerned authorities regarding this either through call or mail.

Hope this helps.