
GM Enaris |

Here's fighter feat progression:
- 1.Improved Shield Bash
1b. Weapon Focus Short Sword
2b. Dazzling Display
3. Intimidating Prowess
4b. Two-weapon Fighting
5. _____
6b. Shatter Defenses
7. Shield Slam
8b. Greater Weapon Focus
9. _____
10b. ______
11. Deadly Stroke
12b. Shield Master
I'm using a short sword as weapon focus to incur less penalty while two-weapong fighting, but at 12th I recieve shield master and that not longer matters.
So my rules question is: Can I swap weapon focus (short sword) at 12th level (using fighter bonus feat swapping) to weapon focus (longsword)?

MechE_ |

As far as I can tell, sure. But, you will lose access to greater weapon focus (short sword) until you hit 14th lv and can swap greater WF SS for Greater WF LS.
I believe this is correct. However, doesn't greater weapon focus also require weapon specialization as a prerequisite? If so, then you'd have 3 feats you would have to swap, one at a time each time you can swap them, in order to get full functionality. IMO, it's not worth the +1 to damage rolls for the transitionary losses.

Rynjin |

You'd have to swap them in reverse order too.
Since Greater Weapon Focus has Weapon Focus as a prerequisite, you'd need to swap Greater Weapon Focus for something else, then swap Weapon Focus at 16, and finally at 20th you could get Greater Weapon Focus again!
My advice: See if you can use the Retraining rules instead.