Uploading Triggers

Say I have 2 triggers in separate .daml files in one project. Triggers A and B.

If I make a change to one trigger, trigger A, I’ll need to run daml build, daml build -o triggers.dar
When I upload this dar file (this dar file contains two triggers), do I need to undeploy an already deployed trigger B?

If by “undeploy” you mean stopping the trigger, it’s not strictly necessary, although if by chance they work on the same contracts they may end up racing over them, depending on the logic implemented in the trigger and the choices you are taking.