TDI injectors are dual stage. Most places don't have the equipment to check both stages, only the primary. In fact I know of only 2 places in the US that claim to be able to calibrate both stages.
Is it necessary to calibrate? Well that can be a heated debate.
A nozzle swap is easy, if you just want to go that route. Unsure where to source the shims and I'm also unsure if IDI shims are the same.
-Todd