Some of the attributes, such as instance size which can be modified during the term; however, the instance type is the one that cannot be modified. User cannot exchange a Standard Reserved Instance, they only can modify it. Reserved RI can be sold in the Reserved Instance Marketplace.
Convertible RI can be exchanged during the term of using another Convertible RI with new attributes including instance family, instance type, platform, scope, or tenancy. Convertible RI Cannot be sold in the Reserved Instance Marketplace.