l want to make a feat that will let you: "gain proficiency in the Deception skill. If you are already proficient in the skill, you add double your proficiency bonus to checks you make with it." 

How to l do this? l know how to add proficiency to a feat,and l know how to give double proficiency,but how do i tell the feat that if they have proficiency,to double it?

We cannot do that at this time without making it as two versions of the same feat like DDB does for stuff like that.

Ah,that sucks. 'Oh,well,at least people can still keep track of that stuff manualy?

Yup, that stuff can be done in the feat as plain txt and manually adjusted on the character sheet.

Can it be done now?

Again, nope.

Damn again.

Currently remaking the Grimhollow transformations as feats on here (not publishing them though). Made the ones that are incompatible with the system on here as their own feats

everybody’s friend (UA) + Diplomat + silver tongue use custom lineage and custom background to get these and you’re good