Total war has a separate exe - it's a copy of the TS game exe, with a few changes, due to hex editing.
He made it so that TS total war reads
tstwr.ini as if it's a rules.ini - this way, you can run TS total war and vanilla TS separately, and not have them interfere with each other (except though that he forgot to rename the language.dll

)
Creagor made a
tutorial on how to do that