Distillers, Rectifiers, Processors, Non Distillery Producers (NDPs), and Spirit Architects  (Oh My !)

Types and Definitions
(1) Distiller 
The term “distiller” includes any person who:
(A) produces distilled spirits from any source or substance,
(B) brews or makes mash, wort or wash fit for distillation or for the production of distilled spirits, other than the making or using of mash, wort or wash in the authorized production of wine or beer, or the production of vinegar by fermentation,
(C) by any process that separates alcoholic spirits from any fermented substance, or
(D) making or keeping mash, wort, or wash, has a still in his possession or use.

(2) Non Distillery Processor or Producer 

(A) In general 

The term “processor”, when used with respect to distilled spirits, means any person who:
(i) manufactures, mixes, or otherwise processes distilled spirits, or
(ii) manufactures any article.

(B) Rectifier, bottler, etc., included 

The term “processor” includes (but is not limited to) a rectifier, bottler, and denaturer.
(3) Certain operations not treated as processing 
In applying paragraph (2), there shall not be taken into account—

(A) Operations as distiller 

Any process which is the operation of a distiller.

(B) Mixing of taxpaid spirits for immediate consumption 

Any mixing (after determination of tax) of distilled spirits for immediate consumption.

(C) Use by apothecaries 

Any process performed by an apothecary with respect to distilled spirits which such apothecary uses exclusively in the preparation or making up of medicines unfit for use for beverage purposes.
So What is Rectification and who is a Rectifier?
Rectification is any process or procedure whereby distilled spirits are cut, blended, mixed or infused with any ingredient which reacts with the constituents of the distilled spirits and changes the character and nature or standards of identity of the distilled spirits.
One example of rectification is, but not necessarily limited to, creating products such as “lemoncello” or “limoncello” in which sugar and citrus products are combined with vodka and stored, initiating a maturation process which consequently changes the character and nature of the vodka, and possibly its alcohol content.This processing can be in the form of infusion, maceration, compounding, etc., etc.,
Another is taking a spirit and re-barreling it in say, a rum cask and aging, adding wood chips, or simply re-barreling and re-aging for a longer period.
The simple mixing of alcoholic beverages with other ingredients for immediate consumption (read cocktails and similar drinks) is not considered rectification.
This is a technical definition of rectification.
In general use in the industry it is also understood to also mean someone who takes bulk neutral spirits and redistills (or tweaks)  them to change their character – usually attempting different cuts to clean or distill them to an even more neutral form, or someone who buys a bulk spirit and makes a minor change to call it their own (creation).
So What is  Bottling and who is a Bottler ?
Bottling is taking a spirit that is in a bulk container (be it a barrel, 200 gallon tote, tank car, etc.,) and bottling or packaging it into a retail form either in an automated or hand bottling line or process. They may filter or blend different bulk containers of the same spirit before bottling but they do not add additional ingredients or treatments to change the character of the spirits.
A bottler is someone who takes a bulk spirits and bottles it.
Spirit Architect 
This is a new term to describe someone who is not a distiller of a spirit but contracts with or directs a distiller to make a spirit for them in specific ways and/or using specific ingredients and/or other treatments, formulas, techniques, to make a spirit to their specifications as directed by them.
This is in some ways quite similar to contract brewing except for distilling and distilled products.It is further differentiated from rectification as the Spirits Architect is involved at the conception or beginning of the product and not taking a product and rectifying it. All the processes are done by a distiller at the Spirit Architects direction or specification.