BUFFY will run fine with BULL DLL, and as Noble noted BUFFY is standalone and ignores the main DLL. What having bull dll active does do is create a "different asset" state with your save. The only problem this creates is if for some reason we need to review a save created with BULL DLL active. We have to have the BULL DLL active on our end in order to open the save. Otherwise though, it is fine, but preferably you would generate HOF games without bull dll active.
Likewise, if you have BULL DLL you cannot open another HOF, GOTM or SGOTM save, because likely those saves are generated by folks that don't have bull dll active. This is due to the required Locked Modified Assets setting. Simply revert to the vanilla bts dll.
If you check the Win 10 thread over in the GOTM forum, and find my post there, I've attached a zip file containing what I call DLL switcher (.bat executables). I use them to switch from bull to vanilla dll. (ignore the one about buffy and steam)
Ofc, hopefully, you did not overwrite the vanilla dll..that would not be good. You'd have to reinstall or acquire it from someone.
(note: Installing BUFFY does not change any vanilla assets..hence, standalone. BUG/BULL installed in Custom Assets essentially does, but only the Custom Assets which can simply be deleted and refreshed. With the exception of BULL DLL which must replace the main dll to activate the features, but the main dll should be renamed with a .extension to inactivate it yet remain available when needed)