If you want the Liverpool ECL kit to show you have to rename it to liverpool_home and replace the current home shirt with it. Though this will cause Liverpool to wear the ECL kit at home for all compeitions.
(If you are managing Liverpool and only want ECL kit to show in europe - switch the home kits around before the european game, then switch skins so the kit you want is showing (when it is switch back), after the game repeat so the league kit is back - then repeat each time you play in europe).
If you want to use the winter ball when its not snowing - save and exit the game, replace the normal ball with your winter ball, reload FM, play the games/months you want the winter ball for, save the game exit. Switch the balls back so the normal ball is the main one, reload FM and continue.
(Its a lot of messing around, but if you really want it

)
Ter - Any chance we'll have competition specific balls or kits in the future (FM2007, 2008 ...) - could have it so that you type in competition ID into the config file, like the year for the changing kits?
Or have it so that the winter ball is used during the winter months (Though is this done in other leagues and countries?)