2 themes and order status

I have a main theme and a mobile theme, auto switching when it detects if its a mobile or not.
when an order is placed, the default status is processing, but I would like if possible to have an additional processing-m option used only when the mobile template is used to make a purchase, this will allow us to track use of the mobile side over the main site.
Is this something that can be achieved, and if so how?

I had thought it would be editing a particular file of the mobile template, but I cant figure out which one or where

Honestly, it's 2018.. if you aren't using a proper responsive theme yet.. one theme that adjusts for all formats, you are just wasting your own time.
You don't need theme tricks to determine if a user is coming from a mobile or desktop. A few simple lines will determine it
https://stackoverflow.com/a/15229056/227664
There are multiple simple options on that link.

For a decent theme, try Journal2. Supported across all versions of opencart, fully responsive, and a ton of builtin modules under the hood.
https://www.journal-theme.com/
Much better than trying to maintain 2 separate themes.

Thanks for the info, and yes I know I do agree, and we use a load of your addons as well, I am in the process of rebuilding using the newer 2 version, time is my enemy, they needed a mobile solution, and I found one that works for the time being.

I think maybe you misunderstood my question. The addon does indeed detect if its a mobile or not, and switches to the relevant theme correctly, but when the user places an order using their phone (and this mobile template) I would like Opencart to use an alternate status from the default "Processing" one to reflect that the order was placed using this mobile theme, basically to find out how many orders are on phones or not.

If you want a insight in how and with what kind of devices your customers are visiting your site and orders are placed, just install matomo (former piwik) and connect it to opencart.
It will give you a very detailed insight in your visitors behavior, used devices, how they go through your site, how orders are placed etc.