[caspar]

Not strictly true afaik? If you own the copyright to the entire codebase you can relicense at will to a different license. (that's what CLAs enable among other things)

Not sure whether you'd still be entitled to the source code under the previous license then.. can a copyright owner revoke a previously issued license to the code? Haven't heard of it, but wouldn't surprise me if it's legal.

[efreak]

Sure, you can change the license, but the old license still applies to the code as it was before you changed it. Assuming you're using a legit open source license the first time around, nothing changes regarding how you can make use of the old code; all they can do is make it harder to find (close the repo) or harder to make use of (squashing/flattening the commits to make it impossible to get the correct historical version), both of which are trivially bypassed by using a third party fork or source release.

[IshKebab]

I am aware, but I don't think that's what OP was talking about.

You can't revoke previously issued licenses (unless the license allows it, which it doesn't in this case).