Change of Inventory Valuation Methods

There is preliminary discussion in our company about changing our inventory valuation method in Sage 100. All skus are currently at Average Cost and discussion is to change to LIFO. I have been looking to find more information on the technical/system aspect on what is involved and more importantly, the  immediate impact on our existing inventory value (I am aware of the pros and cons of the different methods in a financial aspect). There is one school of thought that it will change the value of our inventory going forward...meaning all new incoming/outcoming skus will be valued with the new method and existing skus would be valued at the last average cost amount. I don't know if that is correct and I would be concerned that if it was not and changed the value of the existing inventory, it could be material.

Has anyone experienced a valuation method change?  Can you provide a bit of detail as to the steps and impact...ie change existing inventory or only newly acqured inventory, does existing sales orders/master orders  cogs amount change, ?

Thanks,

Terran