Updating "it" inside a Groovy closure

I have a domain class that is just a list of strings (youtubeLinks).

When saving these links I want to strip out the video ID and save it instead of the entire URL entered on the UI side.

This is what I'm trying (ignore that the regex is flawed)

youtubeLinks.each {
 def youtubeRegex = /v=(.*)/
 def matcher = ( it =~ youtubeRegex )
 it = matcher[0][1]
}

When I save this, it saves the original value of "it". Is there a way to update this reference and have it save properly?

Thanks.