I'm not sure what the 2nd command is supposed to do, but for the first one you can just press R and have the replay reset, then go to the frame that you want to edit.
Press P to pause the replay just before where you want to edit, then shift space to get to it

If the replay speed number isn't greyed out, you can press ctrl and , and have it go in reverse, then shift P to go backwards a single frame

I'm sure having a command would make this easier or just have a shortcut to do it but i don't think it's necessary, people have already done the "R then shift P" to edit specific frames for a long time

Could you explain the 2nd command more? I'm not understanding what you mean