If you're trying to make a pre-facelift X3 look like the LCI version, some parts are easier than others, but none are plug-and-play. There are modifications required for the taillamps, headlamps, grille, and bumpers. I'm sure some of it can be done, but no clue of the expense or time needed.

Interior parts are mostly interchangeable except in regards to the additional aluminium or wood trim on the dash in the LCI models. Those cannot be retrofitted as the dash is a different shape to accomodate the pieces.

Drivetrain parts would likely be different with the LCI models since a new transmission and motor were fitted with the LCI models and share almost nothing in common.