I remember reading about SIA pulling a stunt like that. The odds they gave were something like 35-1, and then AFTER THE FACT when the bet WON, they decided it was a bad line and paid it at 8-1.
There was a long dispute but the player never got more than 8-1 in the end. This is how I remember it anyway.
A top tier book IMO could cancel a future bet with a bad line, but only within a short time after making the bet (if it's a long term bet, then a week or less probably counts as a short time). Proper procedure would be to send you an email with an explanation and an apology for hanging a bad line.
If the time elapsed is longer, then the book will probably have to compensate you for cancelling the bet, like offering a Bonus Play or something like that. If the time is very long, then it would have to let the bet stand. Of course, what counts as short, longer and very long are subjective. Definitely a judgment call depending on the exact circumstances.