Also, if your assembly only has that one difference, you could make 2 assembly items. One with the .1 of the 10kg widget and one with the .5 of 2kg widget. Make sure to name them properly so reps don't get confused with which is which

thanks @jcribb, we would like to avoid the multiple items route as there is about 20x combinations across 3x assemblies already which is looking to increase. I think we will have to go down the work order route