[Script] How to have certain wild Unown forms (FireRed)

[water master 9000]

Hello, I'm wondering about how to make certain Unown appear as in Advance Map, it just has all the forms under one slot. I want to replace each letter sprite with new ones and I want to see if they turn out alright in game.
How can I for example have the B form to appear in a spot?

 

[Sapphire Jester]

Unown's forms in gen 3 depend on its personality value, and in FireRed when a wild Unown is fought, it's personality value depends on which of the Tanoby Ruins it is in, along with the wild encounter slot. Spawning Unown outside of the ruins in FireRed will, I believe, crash the game. Because the forms are all the same species with differing personality values and personality values can't be selected in advanced map, the individual form can't be manually picked in advanced map.

In a way, which form is encountered in battle is already hard coded. The decomp shows a double array is used to decide which wild encounter slots in each of the chambers correspond to a specific Unown form (or more specifically, a value used to ensure a personality value for a specific form will be generated). This means, for example, that encounter slot 0 in the Liptoo chamber will always create an Unown C. Now these array values could be changed to ensure a specific form is seen entirely throughout a certain chamber for testing purposes, though I don't know where the equivalent data in binary is or how it would need to be changed. If that data can't be changed, the best thing you can to see a certain form is run around and fight Unown until encountering the one you are looking for. To follow your example, if you change Unown B's sprite, you'd have get the 2% encounter rate (the last two encounter slots) in the Rixy Chamber.