How do i apply a mirror modifier without restarting my model

I need to apply a mirror modifier to an already modeled mesh, how do I do this without deleting the whole thing.

I need to be able to extrude, move, etc on one side and have it copy over to the other.

Thanks!

- P_enta

 

The best way to do that I know, without using the Mirror modifier, is to select the mesh (in edit mode) you have right now, press Shift + D. Ctrl + M, X which will duplicate & mirror the mesh on the X axis. Afterward, you have to move to where you want it & boom, done

 

Thanks! It works perfectly.

 

I would split it in half and then model. Just be sure to apply the modifier, or in beamng it will be split in half!