I found two logs with significant rot and have cut out and scraped the chips/dust. Until I can get a full replacement job done, can I fill the hole with foam and water putty that dries hard? I saved exterior hunks to then cover the damage until we can get a full exterior job done in a year or two? Is this going to help?
Do not use foams, they trap moisture in. You could after removal of rotted portions spray or brush liquid log epoxy on the cavity. Then dip burlap in liquid and nail it into the cavity. While the burlap is still setting up attach the exterior shell back onto the log. Full replacement is just around the corner.