Other Tab Variant for form depending on grid column value

Not by default. But you can simulate this with a double self reference toggling between reference 1 or 2 using the context procedure. You can then assign a different table variant to the reference. The reference columns are expression columns see the input below. Below is an example: 
 

Ref1 expression column =  case when t1.category = 1 then t1.x_id else null end
Ref2 expression column =  case when t1.category = 1 then null else t1.x_id end

 

Context: 

 

if @reff1 is null
begin
 set @ref_X_X_ref1_type = 2
end

if @reff2 is null
begin
 set @ref_X_X_ref2_type = 2
end