Why not.
If you don`t use it at all or you have any kind of default, banks are entitled to change the credit limit that they authorized, especially on unsecured ones.
But as an individual consumer, what`s the limit one single client may have? And we are all 'Liang Min', guess banks would not spend too much time on us. And they would not ruin their reputation on doing that. They will focus more on the corporate clients and cut their limits on operating lines if they don`t use it or they have lower ratings.
But I guess it would be harder to get new lines.