how can i install/change files through Steam?

Hi all.

once-upon-a-time, before the Steam Era.... (last year)
I had RTW-BI and EB directly on the PC HD, and
i was used to mod some of the files of EB directly from the folder,
usually writing inside it, or changing the original ones with a new ones made by me.
of course, the files were usually the typical wordpad :
-EDU
-EDB
-DESCR_STRAT
etc.

BUT recently, due to: a refreshing of win7=>RTW not working=>keycode not working=> passing to win10=> registering to Steam with a new code ...

I had to deal with Steam

NOW, i have RTW-BI (GOLD) on Steam, along with (the not-played) RTW II. of course, i installed my beloved EB, along with some also loved sub-mods.

But when i tried to install my ....text files (EDU,DESCR_STRAT ETC), they don't work. and the game crashes.

and what is strange, is that some modifications shouldn't bother: e.g. i gave to the triarii the 'phalanx' attribute, but in the game they don't have it (and before -PC HD Era- it worked).

so, how can i install/change some changes in the files of the game?

help help help