if the dpf light comes on and the car goes into limp mode , is it possible to do the 1800-2500 rpm or does it need to be put out of limp mode by a computer ?

As soon it does not go to Safe mode you can regenerate it according manual.

Service shops have procedure how to do Force Regeneration if normal procedure fails...

If you are in limp home mode then you need VCDS or a dealer.

 

The DPF will now no longer be able to regen by itself.

I had an Audi that went to limp mode with glow plug light flashing, problem was a dpf sensor, I drove it 6 miles to the Audi dealer, after about three the fault cleared and limp mode went off, Audi confirmed a sensor fault and replaced it under warranty. I drove it with revs as high as limp mode would allow.