Post #1255: Well I finally found the solution,

📋 Metadata

Well I finally found the solution,
Here is an exemple with solidify modifier if someone else need it

Instead of using
On Invoke :

bpy.ops.object.modifier_add(type='SOLIDIFY')

To create the modifier I used
On Invoke :

a = bpy.context.active_object.modifiers.new("Solidify", "SOLIDIFY").name;

So it create the modifier and the variable a get the name of the created modifier

And now by using
Property:

bpy.context.object.modifiers[a].thickness

it will change the property of the created modifier