If you have a computer at home and the cops think you might have evidence on it of some crime, they ask the judge for a warrant and then they take the machine and they put it in their evidence locker. Then nobody can manipulate it. I mean that assumes the cops are clean, which they aren’t, but it’s not every day that they tamper with evidence inside of evidence lockers.

Or maybe you’re asking about data stored in the cloud, like if you have some possibly incriminating spreadsheet in your Google account. Then the pigs would ask Google to make a copy of the data stored in your account, and Google would probably do that, then sharing the data with the pigs. So if you decided to edit the data later, it would be too late, the copy would already be out there.

Civil litigation in the US has different rules. At some point when you find out that someone is going to be suing you or is in fact suing you, you have a legal duty not to fuck with the evidence that’s likely to be relevant. If it is later discovered that you were fucking with the evidence, then the judge or jury might be able to assume that whatever you touched would have made you look bad. Of course the details matter. But anyway, suppose you want to edit some log file so you SSH into your server and then edit it, but that in turn creates a history of your login and commands that you executed, so then maybe you decide to delete your own history, but then the absence of your history is itself evidence of fuckery… All of that being said, we can be sure that some people are somewhat slick and somewhat lucky and get away with altering data from time to time. We just don’t know how often on account of them not getting caught.