Couple ways. You can try the column editor (Alt+c)
or
record a macro - hit end type the text - arrow down to the next eol
then run macro multiple times (example, for number of lines you have)
Make sure you test on a copy, not the original.
You could look at this one:
http://crimsoneditor.com/Although it's very old, it still works well. The "Column Mode" on it works much better than Notepad++. With it, your edit would take about a minute.
Another tool you might want to look at,
http://www.asap-utilities.com/ You can add text begin/end or anything, when finished, export as a text file.
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