You can take a dry-erase marker, draw over the permanent ink, let it dry for a moment, and then wipe away the "dust." We do that with the Ship Control Cards for Squadron Strike, where you want to erase the vector in one direction and write in a new value without wiping out everything else on the card (accidental pun). You can get felt erasers that snap onto the back of the dry-erase pens to keep things handy. A pack of four erasers is a couple of bucks or so at Office Depot/Max/whatever. There are also pens w/ built-in erasers, but I'm not 100% confident that those won't abrade the surface over time.

http://www.officedepot.com/a/products/586918/KleenSlate-Eraser-Caps-For-Small-Dry/

http://www.officedepot.com/a/products/586900/KleenSlate-Eraser-Caps-For-Large-Dry/

http://www.officedepot.com/a/products/738618/Magnetic-Dry-Erase-Markers-With-Erasers/

http://www.officedepot.com/catalog/search.do?Ntx=mode+matchpartialmax&Nty=1&Ntk=all&Ntt=dry+erase+eraser&N=5&recordsPerPageNumber=24&Ns=p_ZonePriceSort_71|0

On Mon, Apr 20, 2015 at 7:33 AM, Joseph Paul <josephnjody@sbcglobal.net> wrote:

Some thoughts that have occurred to me about using these is that since permanent Sharpie markers are still removable from the drawing surface (alcohol and a little elbow grease) but don't smudge away from use/travel/storage you can do known locations that will see repeat use - like a Type S scout, Free or Far Trader or a small Troop ship for very few tiles. 8x8 means 64 dTons per tile! :) If the players grow out of a ship - scrub the tiles down and draw in the new one's floor plans.