Replacing the second instance of a string within another string.

I am trying to search though a column of data and replace all second instances of a specific string within a larger string. If the second instance isn't there then I don't perform a replacement. What I am finding is the replacement replaces everything in front of the string including the string. Obviously I am missing something with the syntax. Can someone look at the code and inform me what I am missing? Thank you in advance!

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The example workbook lists 5 possible situations that might come up. Only lines 1 and 2 should be changed from what should happen.

The Replace doesn't look right.

Try this instead.

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