Sure you can. Agave is nectar from the agava plant. Agave plant is used to make tequila. It's a sweet syrup much like honey. It's expensive. You can always you sugar. I would suggest a raw cane sugar of some kind.
The thing to worry about when it comes to refined sugar like table sugar is, it doesn't dissolve unless heated. I usually cold brew my ice tea, but if you're going to brew it hot and then cool it you can use any sugar you want.
have you heard of stevia? i have a plant of that im going to throw in the garden, its a leaf, a herb, a natural sweetener, but i dont think it would ever bring up the og on anything unless you had tons, and ground it up.
Unless you're scoring with a diamond or a front-end-loader, you shouldn't damage your bottles at all.