Non-Schengen to non-Schengen are indeed possible airside AFAIK ever since Orly 3 opened. D to D should work fine as well as F to F. If connecting F to D or other way round, you can stay airside but I believe you would need to clear both inbound and outbound passport control as the transfer corridor goes through the Schengen gates. The only case where an airside transfer remains impossible is when connecting to/from the A gates to any other pier, in that case you must exit landside and re-enter airside at A Security.