What I am talking about is the inability to add the Proficiency 'Choose a Kensei Tool' in homebrew. One has to get a copy of the subclass and edit/add homebrew from there. Will there be a fix for this in the future?

This is a homebrew subclass you are making? And you are trying to add the "Way of the Brush" for painter or calligrapher proficiency?

You can just use the Options for it, creating one option for painter's supplies and another for calligrapher supplies.

Edit: I have steps here for adding options to races, the same should apply to classes

Well, yes, it is a homebrew subclass, but the "Way of the Brush" is not the problem I am having. The problem is that I cannot recreate the table of weapons that the Kensei subclass gives for both melee and ranged.

This is due to the Kensei Modifier not being available 

Ah, I get it now. The Kensei subclass uses Modifier -> Kensei -> Choose a Melee Weapon and Modifier -> Kensei -> Choose a Ranged Weapon.

You could brute force it by making two class features at level 3, one for the melee pick and listing as options each weapon that qualifies, and again for ranged.

Well that's going to take a lot of work. Thanks though!