Comment 1 for bug 1162951

Thanks for the report. Some comments:

1) This is already planned and is a step needed for the merging of UltiSnips and snipMate that is still ongoing.
2) You can currently use 'clearsnippets' as first line in your snippet files to clear all shipped snippets.
3) You can also redefine g:UltiSnipsSnippetDirectories and store your snippets in a directory that is not named UltiSnips to avoid sourcing the shipped snippets in the first place. See the docs for this.