Modifying Line of Sight?

I'm trying to make some line of sight modifying abilities in my map. One is a passive ability that increases a unit's line of sight at all times - say, adds 250 to line of sight. (As opposed to the "ultravision" ability that just increases night LoS to daytime LoS only).

The other is an active ability that's cast over an area, and should reduce enemies' line of sight radius to a lower amount (say 350).

How would I go about getting this to work?

maybe adding Ultravision to every unit u want to have reduced his line of sight.

and decrease the ability's line of sight value.

Make abilities based off the Goblin Night Scope item ability and use them (use shift+click for negative values.