Thank you for writing.
In this case it appears to me that the best approach would be to disable the Remove button instead of canceling events. You can subscribe to the SelectedIndexChanged event of the RadListControl in the CondtiionalFormattingForm:
sender, EventArgs e)
ConditionalFormattingForm form = sender
var list = form.Controls[
var removeButtom = form.Controls[
list.SelectedIndexChanged += (s, ev) =>
var item = list.Items[ev.Position].Value;
//determine whether the item was added by you
Let me know if you have other questions or if this approach is not suitable for your scenario.
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