Yes you can be in the parade. you can pay to be part of the Samba schools, wear a costume and march in the parade in the Sambadrome. Try looking up the old episodes of “Lonely Planet”, the guy from Ireland did it. Carnival is amazing. GO!

marck already answered you about the samba schools, also there are lots of blocos carnavalescos (carnival blocks) where you dont have to pay to enjoy it, just follow them over the streets and have fun. hope you´re coming to see it soon :D