So root install location is C:\CFS3 ETO Expansion, if your Hard Drive you are using is C: Otherwise D: or whatever.
C:\CFS3 ETO Expansion\effects\fxtextures is where the texture *.dds files would go, if your Hard Drive you are using is C: Otherwise D: or whatever.
As Capt. Winters said. always back up. It's worth mentioning that it's better to back up texture dds files outside your install as CFS3 tends to search the whole folder for dds files. *.xml files one can just add "BU" or whatever to the end of the file name such as I have "EffectsBUOct2018.xml", and they can stay in the CFS3 folder.