Help with Wild Tables

[Xcisor]

Is there anyway to set a flag or event that permanently alters the wild Pokemon of an area?

Rather than script out a Roaming feature for the legendary dogs, like Lati@s in Emerald, apply Suicune to Route 120's wild Pokemon table at 1% encounter rate, and then once your Pokédex has had Suicune added to it changes the table permanently so that a different Pokemon such as Zigzagoon permanently occupies that slot?

Thanks would help a lot if someone knew anything about this.

 

[Xcisor]

Also if anyone can help, I'm really just trying to get the three dogs, Suicune, Entei, and Raikou to roam in Emerald after the Kecleon/Steven cutscene on route 120.