Yes, I see how white glue would not work. Messy.
Moss takes a long time to rot. A very long time. if you get it from the wild, it should still have a thin layer of dirt on it. As long as there is this dirt, it will last literally for years. Ask anyone who owns a tropical vivarium, it lasts forever. Even in my tropical vivarium, where it is constantly hot and humid, I have had absolutly no problems. I suppose it it was to start to rot for some reason, just pull the whole hide out, then scrape off the scilicone. if you have one of those wallpaper/paint removers, it will be very easy. A small knife would work, too. The nice thing about silicone is that it bonds thouragly, but comes off eaisly with a razor. If you were to start it, you can even just peel it off, nice and cleanly. Even try putting a bit up against your damp hide. you will be able to peel it off. All you would have to do after that is silicone on more moss.
Note- moss takes a lot of water to stay perfectly green. unless you mist it vigoursly every day to every other day, it will be normal to see it browning. I find brown looks best against sand, (what I use for ground cover, no wars on this subject, please) and still looks good against tile or carpet. If, for some reason, you want it gren again after it has browned, all you have to is soak it, and if you keep it moist for three days or so, it will go green again.
I hope this helps.