I guess removing X/A from the file system isn't an option.
No Suppose X has elements ABCDEFGH and Y has AK (Think common config across many vs special config for a device) You may want to say:
BOARD_SEPOLICY_DIRS := X Y
BOARD_SEPOLICY_REPLACE := A
BOARD_SEPOLICY_UNION := KBCDEFGH
BOARD_SEPOLICY_IGNORE := X/A
Drop X from BOARD_SEPOLICY_DIRS
Copy everything down to Y
I don't have any problems with this implementation.
That makes two of us.