Is there a patch that increases the length of command lines?
As in "command lines of the Shell"? Then you don't need one. The shell does not have (anymore, as of 3.9) a command line limit. It can be as long as there is memory to hold it.
On OS3.9 when you boot without startup-sequence, you can not use editpad to edit files and you have to use ed. The ed command cuts of long command lines (like for example by blizkick line which have lots of arguments)
Ed, unfortunately, has a fixed limit of 255 characters per line that is compiled into the code, and the memory for that is not even allocated, but taken from the bss segment of the command, thus just patching would overwrite other internal variables. Thus, there is no way to extend this except to recompile it. But other options exist. CED works fine even without a startup-sequence. (Ed is a dinosaur anyhow, better put it to rest).