I know of others who have, but you can always check with Lyon and Healy.
Also Thormahalen make a “lever gut” string that is easier to play than the concert gut but still has the warmer sound of gut.

I noticed that the older Troubadours were strung with nylon rather than gut.

Yes. The Troubadour can be strung with either, so changing them shouldn’t be a problem. Besides, nylon produces less tension than gut so generally speaking it is pretty much always safe to go from gut to nylon, although not always safe to go from nylon to gut.

Also the Troubadour is made for concert gauge strings, not folk gauge strings, so I would avoid restringing it with folk gauge.

I believe the Troubadour comes with gut in the Fifth octave and nylon in the 4th, 3rd, 2nd and 1st octaves, and that is how they recommend stringing it. However you can restring the entire 5th octave with Pedal nylon if you wish.

I keep the fifth on my L&H Folk harp strung with Pedal Gut and the rest in nylon and I really like the way that sounds. On my Pedal

sorry for the double post, but meant to say, that using pedal nylon for octaves 4 and up is not just more cost effective but pedal nylon is slightly lower tension than pedal gut, and a brighter sound, well suited for folk music, in my opinion.