It depends upon the specific fare rules, the change being made, and when you’re changing it. It can run the gamut from “no changes are permitted” to “all changes require re-faring,” and everything in between. However, it is fairly common to be able to make a change into the same fare class when the first flight coupon is unchanged. So, basically, you can often adjust the return flight of an itinerary for just the change fee if you can find inventory in your ticketed fare class (P, in this case).

As an aside — I really encourage everyone to read the fare rules, especially the changes and cancellations sections, for any itinerary you’re purchasing. I’ve seen LH business class fares that disallow all changes. I’ve seen fares from UA that only allow changes to a more expensive fare — the instructions are to ignore any residual credit rather than to issue an ETC.

It may not be important on a $175 domestic fare that cost less than the change fee, but for international tickets, it’s worth the time to make sure you understand what will happen if your plans do change.