I wouldn't worry too much about making changes, as long as you don't contaminate the water with anything bad and if you get issues are prepared to do a large water change all will be fine. If you get worried about adding something just put up a post here first and wait for some answers as i'm sure it had been done and thought of before.
Well the additional 20 playmates have gone in for over a month and so far I've not seen dead bodies so I guess that is good news. I'm seeing some really gorgeously red ones flit around and water parameters have been perfect. I've not seen more than 10 or so out and about, gonna be positive and reckon the rest are all just hiding.
A friend has gifted me a small little pre-used tank, looks to be 3-5 liters. I'm on the look out for small black volcanic gravel, a nearby fish shop will be replenishing stock of these in a week or 2. I bought a piece of dead coral from them today and drilled some tunnels through. Will boil the coral and leave it to steep in RO water until gravel is available. Plan is to setup the new tiny tank with these and mixed water (old+new) and move some of the chaeto over. Might need to get another led light for it though. I imagine the result should be fairly nice and I now regret not using the black volcanic gravel for my larger tank.