Ive literally just added totally new peat in my chameleons vivarium. Rather that remove it all again, would it be feasible, to "mix" the clay balls through the peaty soil to help with drainage issues that may inadvertently arise?
They're necessary for a bioactive ecosystem. Otherwise you just have dirt and plants that will need to be replaced on a regular basis.
Clay balls need to be on the bottom to create a "reservoir" for water to drain through the soil. Otherwise, you get a mucky mess that will drown your plants. Ideally, you should have a way to drain the water. Otherwise you WILL overwater at some point or another - especIally with smaller cages.
It's a bit of work to set up, but once established there'a practically no maintenance. Either commit all the way to bioactive (drainage, clean up crew, etc), or go barebottom. There's no safe halfway.
Hydro mat? I'm not familiar with this product. Is it a mesh of some sort? If it's a mesh, that's to help prevent your soil from mixing with your drainage layer quite as much and clogging it up/reducing how much water can sit in your reservoir.