OP's biggest problem is that Expedia does permit the change and the carrier now raises medical fitness concerns. Unwinding this scam will take more time and cost a lot more money than the underlying tickets.

Expedia may choose to help OP as a customer service gesture, but it has no obligation to do so. OP is ticketed SNA-ARN. Intermediate connections are connections, not stopovers. If OP has matters to deal with at an intermediate point or a medical need to limit flying hours, those are dealt with by booking point-to-point tickets rather than connections. Those tickets are, of course, significantly more costly.

No one scam really matters. But, the problem is that when people complain that carriers impose unreasonable restrictions or are unfeeling about real life problems, it is scams such as this which lead to bad results.