score:4
There is no mark on the Brazilian visa about which port you are expected to enter from. There shouldn't be any problem with securing different fair. They just don't want to issue you a visa without proof you can leave when you say you will.
Upvote:2
Lately, Brazilian visas are taking more time than expected. So, even with the correct ticket, you may need to change your plans. For US citizen, they will provide a 10 year multiple-entry visa (similar to the visa US provides to Brazilian). So, as soon as you get your visa, you can get any flight you want to arrive in Brazil and leave from any airport you need.