Giving values to [Opt] tags (not changing their names!)

I am sure this is a silly question, but there you are. :-)

The way I understand the [Opt] tags, I should be able to define somewhere one of these tags to some value and every time I use the tag, the actual value goes into the text. So, if I am able to say something like [Opt1] = Bloom2018, every time i insert in my text [Opt1], then I will be seeing Bloom2018.

Assuming I am correct, I don't see how to do it. If I use either 'Rename tags' or 'Preferences'->'Tags", what I can do is to rename 'Opt1' to, say, 'Bloom2018' but then when I select the tag '[Bloom 2018]', insert it into the text and then go to Preview, obviously that part of the text shows nothing because the (renamed) tag [Bloom 2018] has an empty value.

So, how can I specify that every occurrence of [Opt1] should be substituted by the string 'Bloom 2018'?
 
Well, as I said I tried both ways. But I wonder whether I have understood correctly the use of these tags, as per the way I perceive them in my posting.
 
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