Hi there! I'm not sure if you're referring to rolling multiple 401K accounts into various IRAs, splitting one 401K between several IRA accounts, or rolling a 401K to one IRA, then changing your mind and rolling it to another.
However, I can tell you that the once per year rule does not apply to a 401K rollover, and you can roll over multiple 401K accounts (or other qualified plans) to a Roth IRA in a year. These are typically done as a direct (or trustee to trustee) rollover, which means the check is made payable to the new plan, not to you personally. Therefore its not considered a distribution.
(If you do 60 day rollovers, which involve withdrawing funds from an IRA or Roth IRA and depositing it in a new one within 60 days, you would be limited to once per year. The consequence of this would be paying income tax plus a 10% penalty on the distribution, and potentially also an excess contribution penalty. )
