Replace.applescript

app = Application("CotEditor")
app.includeStandardAdditions = true
doc = app.documents()[0]

function replaceSelectedText1(newText) {
	selectedRange = doc.selection.range()
	if(!selectedRange[1]){
		// omit
		return newText
	}

	baseIndex = selectedRange[0] + 1
	numberOfCharacters = selectedRange[1]
	while(--numberOfCharacters > 0)
		doc.text.characters[baseIndex] = ""

	doc.text.characters[--baseIndex] = newText
	doc.selection.range = [baseIndex, newText.length]
	return newText
}

function replaceSelectedText2(newText) {
	selectedRange = doc.selection.range()
	if(!selectedRange[1]){
		// omit
		return newText
	}

	theText = doc.text()
	beginIndex = selectedRange[0];
	afterIndex = beginIndex + selectedRange[1]
	beforeText = (beginIndex == 0)?  "" : theText.substring(0, beginIndex)
	afterText = (afterIndex == theText.length)?  "" : theText.slice(afterIndex)

	doc.text = beforeText + newText + afterText

	doc.selection.range = [beginIndex, newText.length]
	doc.scrollToCaret()
	return newText
}

function selectedText() {
	selectedRange = doc.selection.range()
	if(!selectedRange[1])
		return ""
	return doc.text().substring(selectedRange[0], (selectedRange[0] + selectedRange[1]))
}

replaceSelectedText2(selectedText().replace(/[A-Z]*/g, ""))