Unfortunately, Notepad++ doesn't have a built-in function to split text into specific character lengths. However, you can use a Python script with the Python Script plugin for Notepad++. Here's a simple script:
```python
import os
def split_text_into_chunks(text, length):
return [text[i:i+length] for i in range(0, len(text), length)]
editor.beginUndoAction()
text = editor.getText()
chunks = split_text_into_chunks(text, 65530)
editor.clearAll()
for chunk in chunks:
editor.addText(chunk)
editor.newLine()
editor.endUndoAction()
```
This script will split the text in the current document into chunks of 65530 characters each. Each chunk will be on its own line. Please note that you need to install the Python Script plugin and have Python installed on your machine to run this script.