An amended P35 would be submitted to change payroll details, such as gross wage, employee PRSI class, which had been included in a P35 for a previous year, already submitted to Revenue.
If there was an additional employee to be included the employer would use a supplementary P35, not an amended P35.
The P35 has nothing to do with Vat.
You probably can submit a P35 for 2014 through ROS at this date. I haven't tried as I would always wait until 2015, in case there are unforeseen employee events.