dcf clock
Well, what you are trying to do is not really trivial, at least not if you want to include a way to really set the time. The way I would go at it is to change the subroutine RealTime. This is what reads the time from the dcf77, into vars, which will be used to update your real time clock. Instead of reading the dcf77, you want to read some pushbuttons to update the time.
What you want to do is load the variables minute and hour from a user interface, rather than the dcf77.
The first step should be to display the current time. You could then write a sub to increment each of hour, minute, and seconds, each one checking to make sure you haven't gone too far. For example if minutes => 60, then inc hour by one, and set minutes to 0. You need at least two pushbuttons, one for increment, and one for accept. You read the buttons, and decide what to do, depending on which one is pushed. When you have a routine to do all the increments, then you have to create one to decrement, if you want to have a nice interface. You will also need another push button. These routines will be the challenging part. (At one time I had some assembly to do this, but that was so long ago, and I'm not sure what I did with it, otherwise I'd have included it.)
You will need to de-bounce the buttons before you read them. When the user pushes increment, you want to update the display to show this. When your user pushes the accept button, you then write that value back to the appropriate variable. You can then call the routine SetTime to update your real time clock.
As IanP says, you will free up a couple of pins on your micro, which you would be able to use to read switches. I know you won't have enough pins to read four switches, though, so you may have to go with another method. You could use four (or even up to ten) switches to read a series of resistors and input an analog value, which would only take one pin. Look up AD switches to get more info on this.
I hope you can follow this, and it is helpful. If you have any questions, just ask.
Best wishes,
Robert