Since commit c727cec snippets can't be neither edited nor disabled.
I use my personal snippets for C/C++, because I don't like the style used in the extension's snippets, so I disabled them using the C_Cpp.ToggleSnippets command.

I know snippets suggestion have recently been moved from cpp_snippets.json to the lexer (hardcoded) (see #2942 and #2945). I suggest that you put them in a configuration json file, where they can be edited/disabled (but NOT added, for that vscode has its own file). The lexer could then parse that file and do context-aware suggestions as it did before.