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The lockup only occurred once, so far, and then when I tried again, not all the notes were retagged.  However, I restarted the program, and so far have not been having any issues.
I find I am using version 1.5.6.   I was selecting all the notes, Ctrl+A and then going to Edit, Tag, and inputing a tag (Add Tags)...
Good idea.  If this alarm function, when implemented, was fully configurable with complete options, such as when, frequency/repeat, sound file or pop-up and so forth, I could eliminate a note alarm-reminder program I currently have running, and instead use CintaNotes.
This seems to work sporadically -- at least on my system.  I just tried it three or four times, I found it worked once, then tried it again with mixed results.  On one attempt the program seemed to lock up.  I only tried to tag about six notes.  I'll continue to test this....