Gen 3 : How to generate a PID to get a wanted size?

[Asia81]

Hello,

I pokemon ruby/sapphire, there is 2 npc that you must show a Shroomish and a Barboach of a certain size.
However in gen 3, there is no modern size thing as in the latest gens (as m xs or xl) so it probably must be tied to the PID of these Pokemon.

In this case, is there a tool to manipulate their pid to get the size I xwant ?

[Kaphotics]

Personality value - Bulbapedia, the community-driven Pokémon encyclopedia