According to TAC this is by design. So even if you want to change such trivial setting as MTU on a VPC you better do this off hours. I feel this is a limitation that should not exist in NX-OS. There's got to be a way to make trivial VPC changes without dropping traffic. There should be like a 1 minute window or something for you to make change on the second switch, or maybe some kind of automatic configuration replication to second switch (similar to VSS).
One clarification on changing paramaters (e.g. MTU) on a vPC on N7K:
During a configuration change on a vPC, one vPC peer conveys configuration information to the other vPC peer in order to verify that vPC member ports can actually form a PortChannel, which is the consistency check. As an example, if two ports that are going to join the channel has different MTU settings, even for a short duration, this is a misconfiguration.
Depending on the severity of the misconfiguration, vPC may either warn the user (Type 2 misconfiguration) or suspend the PortChannel (Type 1 misconfiguration). MTU is Type 1 parameter therefore changing its value would cause the vPC to be suspended, therefore service disruption. One can use "show vpc consistency" global or interface to check the type of parameters to be configured. The link below gives more details on the consistency check:
We are pleased to announce availability of Beta software for 16.6.3. 16.6.3 will be the second rebuild on the 16.6 release train targeted towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are looking for early feedback from custome...