Edit: Thanks for your kind comments on disabling contributions. I'm aware of the possibility, this is just a meme.
Contributions in open source projects are great, needed and make the world a better place after all. Therefore they should be declined politely, optionally by giving a reason.
I hereby inform you that I will no longer accept contributions to this post /s.
Is archive mode the appropriate tool for this? I would assume that's for when a repo is no longer receiving any updates from anyone, not just when the owner doesn't want others contributing.