In an interlocutory decision, the Board of Appeal in T1427/09 decided that filing appeal documents using the wrong electronic signature (the wrong smart card) may be remedied under R.50(3). The signature of someone who is not authorised is considered to the same as omitting the signature.
PCT is rather compicated, which makes any overview particularly helpful. I recently discovered this very useful document and presentation on the WIPO website. In particular, the document (starting on page 27, has a very nice summary of “Procedural Safeguards for International Applications”. Several of these have been on the EQE before.