The TSA will DEFINATELY forbid cockpit jumpseating into the US. Since PR is a US territory, that might be different though. Some airlines forbid cabin JS-ing on international flights also.

You should really ask the airline you're going to use...I would go to the ticket counter or gate and ask them. These kinds of policies tend to be enforced inconsistently, and the gate agents may do somethong other than what the policy manual says.