Are there rules for creating a new feat as there is for creating new spells and custom items?
Are there rules for creating a new feat as there is for creating new spells and custom items?
Not really, but it's not inherently difficult.
I'd try to configure what it is you want the feat to do, and then look for any similar connections, if any. If none, then it's fine to make it as-is, assuming it falls in line with the general strength of a given feat.
For example, I was constructing an Unchained Fighter class which uses Stamina as a class feature (and not the generic Stamina system). This resource is similar with Ki, Arcane Pool, etc. Some Fighters may struggle with Stamina, especially early on, so I decided to create a feat that provided a static increase to their Stamina points.
There were feats such as Extra Ki and Extra Arcane Pool, so I modified and configured the feat to grant 3 Stamina points, and it can be taken multiple times, similar to the reference feats.