The Factory API does not give you the control of the visibility. But there is an other option. the floor and grid objects are part of the "ClientGraphicsCollection". You can control the visibility from there. I've tested this on new and exsisting factory designs and it worked. You just need to implement the lines in your own rules.
Dim oDoc As AssemblyDocument
oDoc = ThisDoc.Document
'//// Grid /////
'Grid on
' oDoc.ComponentDefinition.ClientGraphicsCollection.Item(1).Visible = GraphicsVisibilityEnum.kAllGraphicsVisible
'Or
'oDoc.ComponentDefinition.ClientGraphicsCollection.Item("3C19E8F3-B3E0-41d2-9274-DBF361F7B571").Visible = GraphicsVisibilityEnum.kAllGraphicsVisible
'Gridoff
'oDoc.ComponentDefinition.ClientGraphicsCollection.Item(1).Visible = GraphicsVisibilityEnum.kNoGraphicsVisible
'or
oDoc.ComponentDefinition.ClientGraphicsCollection.Item("3C19E8F3-B3E0-41d2-9274-DBF361F7B571").Visible = GraphicsVisibilityEnum.kNoGraphicsVisible
'//// Floor //////
'Floor on
'oDoc.ComponentDefinition.ClientGraphicsCollection.Item(2).Visible = GraphicsVisibilityEnum.kAllGraphicsVisible
'or
'oDoc.ComponentDefinition.ClientGraphicsCollection.Item("D528449B-0FDA-4f04-A0EC-437F6C8E404D").Visible = GraphicsVisibilityEnum.kAllGraphicsVisible
'Floor off
'oDoc.ComponentDefinition.ClientGraphicsCollection.Item(2).Visible = GraphicsVisibilityEnum.kNoGraphicsVisible
'or
oDoc.ComponentDefinition.ClientGraphicsCollection.Item("D528449B-0FDA-4f04-A0EC-437F6C8E404D").Visible = GraphicsVisibilityEnum.kNoGraphicsVisible