HI,
the FX rate type "P" is picked from the CO planversion entered in S_ALR_87099918 (RAKOPL02). Thus create a CO planversion "XY" with the FX rate type for your "historical date", and transfer the depreciation plan data to this CO planversion "XY".
After that copy the plan figures to the CO planversion where they are needed by using planning copy functionality (T-Code KP97).
BR Christian