I have prepared a sample project showing how to remove the CellEditUILayer and add a custom UI layer that uses a RadNumericUpDown as cell editor. You can find it attached.
I have found a bug while preparing the sample project that prevents the change of the active cell mode to Edit when the CellInputUILayer is removed. The bug is fixed and the fix will be available for download with the next LIB that will be released next week. Please bear in mind that the demo project will not enter in edit mode if you double click a cell until you update your binaries.
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