You can insert a table and that will probably ungrey the icon. Or you can insert a note and put a triangle border around it.
But why would you want a rev triangle without a table that explains what that triangle is?
The short answer is "NO". The revision symbol is driven based on the rev
from the inserted revision table. Another point to know is if you do place
rev symbols on your drawing and want to delete one, it will not allow you to
delete just one. It will force the issue of deleteing all of them and if you don't select
properly, the rev table can be deleted as well.
So with all of that said, my suggestion would be to either create with skethced lines
and text to formulate a block, or create the rev leter and in the property manager
select the boundary of a hex. At least these methods will allow you do do as you described above.
Also take a look at my own thread that speaks to my own issues with the rev symbol.