Re: lg g2 had upgrade with new icons can I go back to old icons
If the launcher you're using takes different icon sets, just find one you like and install it. If not, find a launcher that does and an icon set that you like. Installing a launcher and installing icons is the same as installing any app.
If you mean pull the icons out of the old version and put them into the new version, it can be done, but you have have enough programming experience that you wouldn't be asking.