Is it permissible for someone who has sinned and repented to deny their sin if asked about it, for fear of being accused of other things they did not commit?

The lie of a repentant person to conceal his sin is permissible because it is among the things that have been granted a concession for. It is analogous to what is explicitly mentioned in the texts regarding matters in which lying is permissible, such as denying a sin to cover for its perpetrator, as long as he has not committed it openly. The better and more preferable approach is to use ma'areed (euphemisms/double meanings) in denial, such as intending that he did not commit it at a specific time or in a specific place. Indeed, ma'areed provide a way out of lying. His lie is permissible whether he fears being accused of something he did not do or not.