FAR 6.302-1(c)(1)(ii)(A) states: "If only a portion of the acquisition is for a brand-name product or item peculiar to one manufacturer, the justification and approval is to cover only the portion of the acquisition which is brand-name or peculiar to one manufacturer. The justification should state it is covering only the portion of the acquisition which is brand-name or peculiar to one manufacturer, and the approval level requirements will then only apply to that portion."  The justification and approval requirements of FAR Part 6 apply unless one of the exceptions at FAR 6.001 applies, so be sure to review the exceptions. Pay particular attention to the exception at FAR 6.001(c): Does requiring a brand name card reader change the scope of the contract? That is subject to contracting officer determination. I recommend reading the summary of how GAO considers "in scope" vs. "out of scope" at this link.  If it's decided the change is out of scope, and the card readers are commercial items, then the requirements of FAR 13.501(a) would apply.