I use enums to workaround that
metaball_color := enum:
White
Blue
Red
(Wrapper: metaball_color).GetMaterial():material=
case(Wrapper):
metaball_color.Blue => M_Metaball_Blue # Your texture/material
metaball_color.Red => M_Metaball_Red # Your texture/material
metaball_color.White => M_Metaball # Your texture/material
Then you can set
@editable
MetaballTexture : metaball_color = metaball_color.White