No, you have to choose a Role that corresponds to your character because the role card essentially replaces the Power section of your character card. You choose between the two Roles available for each character.
What pluvia33 said. You must pick a role that goes with your character and came from the same source as your character card. So S&S Valeros can't take the RotR Valeros role cards.
Each character card has a corresponding role card, though you won’t use it right away. Role cards are part of the reward you get for completing the third adventure of the Skull & Shackles Adventure Path. Role cards offer new feats for you to choose; these feats apply to your character as if they were part of the original character card, and your role card counts as part of your character card.
Each side of the role card presents a different specialization for your character, allowing you to choose one of two different paths for your character’s continuing advancement. For example, one side of the role card for the oracle Alahazra presents feats that let her specialize as a visionary stargazer, while the other side offers feats to advance her as an offense-oriented tempest.
When you are told to select your character’s role card, select one of the two roles. From then on, whenever you gain a feat and choose to check a box on your role card, you must always choose feats from that side of the role card.
Your role card is designed so you can place it directly over the Powers section of your character card. When you first get the role card, check any boxes for the role you’ve chosen that match boxes you’ve already checked on your character card. For example, if the “Light Armors” box was checked on your character card, check the “Light Armors” box on your role card.
So your character has a particular role card corresponding to their character card. And you place it right over top of the powers on your character card and transfer the boxes you've already checked off. So not only do you have to select their corresponding role card, but if you did select one with different powers, you'd have not boxes to check off.
When the same character appears in different sets, they are represented with different cards having different abilities and powers. For example, among other differences, the rogue Merisiel has the Craft skill in Skull & Shackles and the Perception skill in Rise of the Runelords. To distinguish between them, we add the Adventure Path name to the card name. For example, “Rise of the Runelords Merisiel” is a different card than “Skull & Shackles Merisiel,” so you may not exchange feats or role cards between them.
So while cards do what they say, they do so with in the context of the rules.
Interesting idea though, playing with the wrong role card. Which one in particular were you thinking about mixing up?