In a PowerShell script, to replace the first occurrence of a string in a file I came with the code below, which keeps track in a variable whether the replacement was made.
If it is xml, handle it as xml:
$xml = [xml](gc $original_file)
$xml.SelectSingleNode("//version")."#text" = "6.1.26.p1-SNAPSHOT"
$xml.Save($destination_file)
SelectSingleNode
will select the first version element. Then replace it's inner content and save to the new file. Add a check for the inner content being 6.1.26.p1
if you want to specifically replace only that.