Cross flash a t-mobile stock (pre-rooted) ROM to G900P

Has anyone here tried a G900T ROM on their G900P? I'm curious whether this can be used to enable wifi calling.
(Just the system zip, not bootloader/kernel/modem, of course). I recall reading a thread on cross flashing with all kinds of info on doing this but I can't for the life of me find it again.

Am rooted and have TWRP.

Thanks!

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