Mixed MU consists?

[Baldy's Boss]

When I use the 2cc EMU wagons I can refit the train to passengers or mail...but is there a way to have both passenger and mail units on these trains or must a train be all one or all the other?

[NekoMaster]

When I use the 2cc EMU wagons I can refit the train to passengers or mail...but is there a way to have both passenger and mail units on these trains or must a train be all one or all the other?

When refitting trains, you can click on individual cars/wagons in the window and refit that car to what ever it allows.

[Eddi]

if the GRF coded it as articulated vehicles, you can only refit the whole thing

if it's double-headed with wagons dragged in, you can select individual wagons to refit.

[Transportman]

if the GRF coded it as articulated vehicles, you can only refit the whole thing

if it's double-headed with wagons dragged in, you can select individual wagons to refit.

The 2cc set is coded as double headed with wagons dragged in, so individual wagons can be refitted.

And as an addition on what NekoMaster said, using Ctrl+select will also select all wagons behind the one you selected.