Removing repository but keeping the app?

I have downloaded Veracrypt and Firefox to my machine. Is it possible to delete the repositories for these two programs but keep the apps on my machine? PureOS won’t let them update through the repositories and I don’t need them to anyway.

If so, how do I go about doing that? I’m pretty new to linux so any help would be appreciated. Thanks!

Open the software update program, and go to other sources (I think that is what it is called), then just delete those repos.