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I'm not sure why it would have this limitation. Maybe it's just to prevent a crash, in case someone asks Inkscape to do more than it can handle?
I think you should be able to put a minus sign, somewhere in the dialog (where currently it's a positive value). I'm not sure exactly how you have it set up, so I can't say exactly what needs to be changed. But anyway, I'm thinking just set up another circle, and clone lines in a separate process, that will fill in the gap. Then just move the new lines into the gap.
Oh! Or even easier, duplicate the same section of lines from the right side, and flip them around and move over to the left side.
To get it fixed in future versions, you'd need to make a bug report. (Even if you think of it as a feature request, the report still goes in the same place.)
https://launchpad.net/inkscapeHhm yes, I see that Inkscape won't let you enter a number larger than 500. I wonder if it also limits the width/height values.... Looks like it limits the w/h to one million px.....which makes the 500 row/column limit seem pretty low.
There may be some reason for the limit, but you'd have to ask developers. If you just want to know why, probably the mailing list would be the best place to ask. But if you want it changed, the bug report/feature request is the best place.