[Theisey]

I took a different approach...

At the time I was working mostly H and some L so I had at least two shirts (lets just talk SS type).
Once the schedule as out, I found I was working several games as a B, and S and finally an F.

So, I simply just bought the additional plackets and sewed the one I needed over the H or L with some black button thread with using looping stitches about .5 inch apart all the way around with a couple in the middle.
This worked out very well for my purpose and was far far better than the Velcro I saw guys using.

I'd do this the night before, but at one game where I was sure we would be wearing LS shirts, I had to do a 5 minute sewing job during the pregame to my SS shirt. I kept the stuff I needed in my bag a this was an easy task to do.

I do echo the rest... stay away from the Velcro. You might try double stick carpet tape, but other than for use on a flag patch, I did not try it though I heard it did work OK.