How do you use Notepad++ regex pipe | for strings longer than one character?

It's nothing special about "longer than one character", Notepad++ doesn't support the | character in regex. Not even "a|d" works. See the regex help page. Version 6.1.1 of Notepad++ now supports |.

I'd suggest using an editor with a proper regex implementation like gvim or UltraEdit.

Upgrade to Notepad++ v6. From the changelog: "PCRE (Perl Compatible Regular Expressions) is supported." I've verified that | works in regex search when using Notepad++ v6.

Inside a character set declaration ([…]) only the characters \, ] and - are special characters with the special functions of escaping the next character, closing the character set declaration and marking a character range (only if not written at the begin or end), respectively. Any other character is interpretet as a plain character.

So is your | in [a|d] which means that [a|d] describes any of the characters a, | or d and not just a or d like a|d does.