I needed a coil one day, and put a 12VAC coil that was in the oddments collection, onto the valve as a temporary coil to get the line up again. It was actually running on 24VAC, but as it was operating for 1 second every 5 minutes I figured it would do until I could get the right coil along with the right valve body. I never actually bothered to change it until I was replacing the air piping a few years later...........
Note, the newer generation of Festo valves are a lot less reliable than the old ones. I use Shako where I can not use Numatics, as those are nice, plus you can buy a rebuild kit for them that is cheap and which works. Some of the Numatics valves have 20-30 million cycles on them, and as I needed one rebuild kit for that size I spent 20 minutes extra and rebuilt the other 3 in that spot as well. Just o rings and plastic buffers, and only the o rings were brittle and the one buffer had disintegrated. Bought 4 kits but there are so many rubber parts in the kits I actually only used 2, with all rubber and plastic parts being changed out of those 2 and even had left over parts. They include a set that covers the most complex version of that style, and mine are the base model.