A parachemist, in this sense, is one who is working on issues that are related to, but not identical to classical chemistry.
Classical chemistry, as we know, involves the interactions of chemical elements, based on the properties of such elements.
Para-chemistry involves both the interaction of chemical elements, and other significant properties, such as in this case also their nuclear/radioactive properties, which may affect their chemical and physical interactions.
For example, regarding one use of the terms ortho/para chemistry see: aanda.org/articles/aa/full/2006/14/aa4420-05/… in which it states: " For each isomer, two equivalent H nuclei, of spin 1/2, couple to generate ortho (nuclear spin = 1) and para (nuclear spin = 0) species with spin statistical weights of 3 and 1, respectively. " as an example in which para chemistry is tied to the nuclear properties of the interaction.
Another example of para chemistry referring to a non-classical chemistry understanding: arxiv.org/pdf/1612.07845.pdf refers to the idea that deuterium can have 3 spin states, and thus the parachemist may need to understand such spin states, as well as the classical chemistry, in order to analyze a chemical reaction.
" D 3 + has three spin states i.e. ortho (I=1,2 and g I =16), para (I=0, g I =1) and meta (I=1,3 and g I =10). "
As another use of the term tied to its connection with properties other than purely chemistry concepts, this paper [ingentaconnect.com/content/jswt/jswt/2011/00000037/00000001/… states:
"Para chemistry covers the manufacture of products for specific uses such as, for example, agro-chemical products (insecticides, herbicides, etc.), explosive products, maintenance products, painting products, etc."
Here, I believe from my talks with industrial chemists, that the term refers to the notion that for industrial chemists, non classical chemistry concepts such as price, availability, ease of use etc. all play an important role, and not solely the classical chemistry.
Papers also exist that reference biological toxicity as a factor considered in the para-chemistry of a chemical reaction.
In an analogous way, the term ortho-chemistry, as another example, may refer to both the interaction of chemical elements, and their spatial configuration and properties, which may, in turn, affect their chemical and physical interactions.
The term ortho-para-chemistry can refer to an understanding that involves three different types of properties -- the chemical properties of the elements, properties of their spatial configuration, and their nuclear properties.
Terms such as meta chemistry also exist, and, as with the term para-chemistry, the idea expressed is that concepts and properties that are important to an understanding and analysis of a chemical reaction or sample may involve other properties outside of chemistry, but that are highly important to such analysis and understanding.
Such properties may involve the nuclear or radioactive properties, the spatial properties, the toxicity or biological properties, or others, including industrially important properties, such as scarcity or technical difficulty.