Any polish should do, but you may need to dye first (Fiebings would be a good choice here) if there is a major colour difference over a large area. Matching the colour exactly could be a challenge.Wouldn't you have to neutralise the chemical before applying the dye or polish ?It may be better to wear more appropriate footwear - some natty wellington boots perhaps
I made my own greenland wax and used it on my medium field bag - http://www.styleforum.net/t/133759/filson-bag-thread-with-pictures/3675#post_7059688I found bars of the Gulf paraffin wax at Walmart and the beeswax at a farmers market.
The April catalogue has some interesting pages about the materials, the manufacturing process and repairs - http://axiom.ipaperus.com/virtuoso/Filson/April2014/
No details on the Filson X Magnum bags, just a teaser page ...