Converted to tubless a while back, when I got my Enve wheels. Since my Ignitors still had life in them, I just remounted them with Stans. It took about a month for them to be fully sealed and hold pressure for anything longer than about 12 hours.

This week, I noticed they were a bit tired and, getting ready for a 3 day trek on the Kokopelli Trail, I decided to replace them, just to avoid any issues and make sure I had the best possible treads.

Put them on last night (and for the record, there is no floor pump in existence that will seat the beads on these things!) and so far, it looks like I have no loss of pressure, no wet spots on the tire and nice new treads.

I've seen lots of threads about converting, but I don't recall any specifically saying do it when you replace tires, so never thought it would be an issue. Using old tires works, but takes time to seal up, adding sealant and lots of pumping and spinning the tires whenever I walked by the bike in the garage.

So my lesson learned is to do your conversion in conjunction with new tires if possible.