P3D SET AS PRIMITIVE PARTICLE
That commmand will force the particle set to go back to primitive mode. but, if you setted it to use a preset mode, it will use some of the old preset parameters. You'll have to entirely delete and create the particle set to mae it really becoma as primitive mode.
SYNTAX
P3D Set As Primitive Particle IDParticle

ADDITIONAL INFORMATIONS
3D PARTICLES Commands Menu
Index
SAMPLE
Demonstration Sample