Hi Alan,
I have, in several similar situations. I learned it from a class done by Bruce Stevens and Steve Schell at a conference years ago. I recommend a conservative approach, with controllable amounts of moisture. I used wet T shirt material, fairly wrung out, a narrow strip (1/4") at top dead center on the hammers. Use a hot iron for a few seconds, level, to drive steam straight down and in - when the moisture is gone, it's gone, so you can't overdo it. Don't rock the iron, it can puff out the shoulders. Be prepared to do a light filing afterward if hammers look shaggy at all. (It's ideal to steam first, on a set of hammers that are flat on top and need a good filing anyway.) I would then go back and repeat on individual hammers or sections if it wasn't enough, or use cloth less wrung out.
My theory is that sheep's wool is like my hair, it curls up when it's damp. I felt like it revived some of the springiness or resiliency of the felt. Be aware that while hammers are still damp at all, it will sound like you went too far. With drying time and a tuning, a lot of sound will return, and may return unevenly. So do the steaming early in a service call and tuning. You can voice as normal if a few notes come back too much.
Let us know how it turns out! Plus, what's to lose? If the results aren't good enough, you still have your other options.
Kathy