without registering for 1st round can i register for 2nd round in Maharashtra state counselling of neet ug

If you didn't registered during the 1st round of counseling the yes you can register during the 2nd round of counseling. Do remember you register as soon as you can as the form is useful till you clear your graduation.
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If you are talking about participating in counseling then yes you can skip 1st round of counseling and participate in 2nd or 3rd round of counseling there's no problem in such thing.