Change one number in a calculation without reentering everything?

[userx14]

Hello Forum,

if I have a equation which is quiet nested, and I realize that one number in the calculation was incorrect, is there a possibility that I can modify the number after i have already finished the calculation?
I tried it on a Hp 50, but the "undo" button only reverted the calculation by one step.
On my fx9860g I could just edit every part of the equation and press enter to get an updated result.
Is this possible with RPN?
Can one undo to a certain step an then redo the calculation with a simple buttonpress?

I'm sorry if the answer is obvious, because I'm new to Hp&Rpn...
Thank you for your answers.