Is there a way to save and re-load flight plans?

I dont know about 3rd party planes like the CRJ but I do fly the stock CJ4 a lot & one glaring issue I come across is that a save flight has these negative traits:

  1. It does not preserve the flight plan. You wont see the plan on the displays.
  2. Autopilot is off, you have to quickly turn it on.
  3. Weather and clouds are locked, you cannot change them.

Others have explained how to save and load the plan from the world map. Have you tried the excellent free LittleNavMap? It is much more flexible and easier to use than the in-game system. You make the plan, export it in MSFS format and then just load it in the game using the same method @BriL0ve has shown.

EDIT:
Ignore everything I said! I am talking about saved flights (.FLT) , I just realized you were talking about plans (.PLN)! What I said applies to loading a saved flight.