I don’t know if this method (from this post) works on a P1x, but it does with my non-AMS X1:
First, slice the model. Then, on the right-hand side of the screen when viewing the sliced model, there is a slider that you can slide down and watch the layers of the print disappear. Once you get down to the layer immediately preceding the filament change, you right-click on the + of the slider and say “Add Pause” then you re-slice and send to the printer. (I imagine if you have multiple changes, you can add multiple pauses, but I have not tested).
I found that after pausing, the X1C screen would not let me do anything but resume the print, but I could use the Device tab controls in Studio to manually unload/load the filament.
I also found that I occasionally had a small layer shift after changing filament, which was cured by inserting this g-code at the correct layer, instead of the pause.
M400 U1 ;pause
G28 X ;home
There have been multiple upgrades to Studio and firmware since I did last did this, so I’m not sure if the g-code is still necessary