. You can eventually change its dimesions with STTY, but it's verily not recommended.
Other than the hassle of having to do it, there's absolutely nothing wrong with adjusting the terminal size if you want over LISH. Terminal size is just a setting like any other; you don't hurt anything by changing it. True, as an virtual serial port LISH misses the automatic communication about size changes we've all grown to expect over other connections, but that certainly doesn't mean it can't handle different sizes.
I do agree with the point that there's little reason to use LISH if you have normal network access to your Linode, but if you do have to work through LISH, no reason you can't be comfortable and use a virtual console with large dimensions, or just ensure apps through LISH wrap properly within your client window.