The answer highly depends on which client you use.
Command Line Client: by default, the command line client does not include externals during commits. From the SVN book:
[...] if you want to commit changes that you've made in one or more of those external working copies, you must run svn commit explicitly on those working copies — committing on the primary working copy will not recurse into any external ones.
TortoiseSVN: In the commit dialogue, you can easily deselect files from externals:
PhpStorm: I cannot tell here, since I don't know the IDE personally.