Is it possible to add a custom range, for the in-range check?

Like on Classic all players use 40 yards, but as a mage, you want to check for 30 yards.

Yeah, i don't have any up-to-date docs on advanced customization ready, so basically install this thing and put inside the spellID of your 30yd spell
AptechkaUserConfig.zip

Or wait, are mage buffs also 30yds? I should probably make that a default then
EDIT: Done

nice, perfect! btw priest spells don't work on a mage I use this spell Dampen Magic (30 yards)

maybe check this library out LibRangeCheck-2.0, so you don't need it specifically for a class and the players can choose a custom range