Getting any kinds of spell/fire/fog/whatever effects from especially WoD+ to WotLK often results in huge loss of quality or produces something, what can't really be used at all, because WotLK doesn't support some of features introduced in later expansions. I don't know how much does this apply to Cata though.
Wheter it is possible - yes, it probably (not 100%) is - but thats universal answer to all "is it possible" questions around here. Just note that it may not be worth actual result. You can certainly try. In case of WotLK, SpellVisual*.dbc are responsible for spell visual effects. You'd have to figure out how whole system works, retro-port Legion M2s you want to use, get them into corresponding DBCs on older client and link them to your new spells. Also, if there is some crazy system on Legion putting spell effect M2s together which works in completely different way than on WotLK, this may not be really doable at all.
