Can You....

...silicon down something on your shiny fiberglass and later peel it up and have no damage to your boat?

Sometimes yes and sometimes no. I have had good luck taking gps antennas off until the last time I removed one. There is still silicone on the gunwale and nothing I have found will remove it.

Sometimes silicone is too good and hard to get back off. I would try double stick tape. 3M makes some great stuff and the adhesive could be easier to remove than silicone.