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I am trying to replace a period with a colon within a time stamp but without effecting other periods in in the text.

<trkpt lat="31.579166667" lon="120.295263333">
<ele>24.533331553</ele>
<time>2007-05-05T11:20:57.927Z</time>
</trkpt>

In the <time> row I need to change the last . to : this has ...