In Wotlk and Below, most of the actual non visual spell info is in Spell.DBC. in Cata, they split the spell information across several DBC files. Odds are you are missing the correct data in a different DBC when you change the spell id.As for custom spells in Cata, I wouldn't say impossible, but honestly I haven't done anything more than some surface research on custom spells.
Did you edit spelleffect.dbc also? That dbc controls the actual effect of each spell. This one is different. It doesnt get called from spell.dbc, but rather the other way around. Spelleffect has a column for the spell id its attached to.