They can make it interesting by showing Radhika's shock in the beginning and then questioning her fate and inner feeling. Since she would now meet Rohan and won't feel anything for him, she has to question whether he is really KK. They can even close a loophole where she sees that Dev was mistaken as Rohan in that contest and he won it by playing flute. So her feelings for Dev and subtle hints should lead her to question if Dev is indeed the KK and they switched that day. So she has to investigate the truth. She may be unable to tell it to Dev for now as he agreed to marry Chanda and everything is a mess.
But creatives, show Radhika taking a proactive approach in deciding whether she is marrying the right person and if he is not the right person, what she needs to do. You can make the story interesting. Audience liked Dev in CB1 because he was shown as a strong person who trusted his inner feelings. So despite thinking that he married Vishaka by mistake, he never accepted her as his wife and always fought to get back Radhika in his life. So show that Radhika here does the same as she is the one with all the facts and have her father's backing in going after the person she loves.
Am wondering if the ratings and feedback had some impact. Because they were keeping it a mystery and now suddenly disclosing everything with Dev knowing Radhika's name and Radhika knowing the truth about her groom. Hopefully they will now show her knowing the names too.