Does anyone know if a plan is or is not allowed to designate different beneficiaries for different sources (1 beneficiary for 401(k) deferrals and a different beneficiary for profit sharing)? Any cite?

There wouldn't be any legal restrictions on this practice (sorry - no cites), but it would be an administrative nightmare, especially considering some of the state laws out there dealing with beneficiary redesignations upon divorce (even considering the recent supreme court decision). Keeping up with one beneficiary for each participant is difficult enough, isn't it?

Yes, it is difficult enough to keep up with beneficiaries. I was hoping I might be able to tell an employer it could not be done, instead of having to convince the employer that it is a bad idea. Thanks.

The part of the required distribution rules dealing with separate accounts recognizes that a participant may name different beneficiaries for different accounts in a plan.