Bonus Election When Paid w. Regular Payroll

Feel like I remember this coming up before but now I can't find anything. 

Bonuses not excluded comp.

Employer pays a bonus, NOT off-cycle (i.e., paid with a regular paycheck, so EE just gets a larger paycheck for that pay period). 

Say Employee A has a $100/paycheck deferral election. Employer should just withhold "Normal" election correct? Since it is being paid in a regular paycheck, there would not be an increase in deferrals withheld?

That sounds appropriate, but really comes down to the Plan Administrator interpreting the document and its standard operating procedures conforming to Its interpretation.

So if the bonus were a separate paycheck, he'd have gotten $200 total that week, I suppose.

Many pre-approved documents (which is about all I see these days) have a specific Administrative Procedures addendum that specifically deals with questions like this - Relius does, for example. Take heed of Bri's comment. 

When a plan-documents set includes, beyond the Adoption Agreement, a “Special Effective Dates”, an “Appendix” (or a few of them), an “Administrative Procedures”, and perhaps other differently labelled sections, which of them is treated as a part of “the” plan document?

May a user decline to fill-in all or some of these parts without losing reliance on the IRS’s opinion letter?

May a user change the text of all or some of these parts without losing reliance on the IRS’s opinion letter?

Or if these extra parts must be parts of “the” plan document, why are these parts differently labelled and not a part of a whole Adoption Agreement?

Here's the wording on our document, FWIW...

The following are optional administrative provisions. The Administrator may implement procedures that override any elections in this Section without a formal Plan amendment. In addition, modifications to these procedures will not affect an Employer's reliance on the Plan.

Thanks!