How to change a *VectorProperty size? Let's say I've created a scene property named a:

bpy.types.Scene.a = bpy.props.IntVectorProperty(
    name='a',
    description="Frequencies",
    size=2,
    default=[1, 2]
)


And now I would like to update it's size to something else.


How can I do that?
Do I have to override the property? What if instead of a single property I have a PropertyGroup and I want to update an IntVectorProperty that belongs to the group?
Have you seen Property Definitions? IntVectorProperty have other parameters to define, among which no "size"!

You can create a Custom property from PropertyGroup:

class CustomProperty(bpy.types.PropertyGroup):
    name: bpy.props.StringProperty(name="Name", default="Some name")
    description: bpy.props.StringProperty(name="Description", default="Frequencies")
    size: bpy.props.IntProperty(name="Size", default=2)


To update any property just assign some value:

bpy.types.Scene.a = 3